Category Modern Science

What are Asteroids?

ASTEROIDS

Asteroids are small, mostly rocky, irregular-shaped bodies. They are found orbiting the Sun in a band filling the 550-million-kilometre gap between Mars and Jupiter. The largest, Ceres, measures just under 1000 kilometres across, but only a handful have diameters greater than 100 kilometres. About 4000 have been recorded, but there are many thousands more too small to be identified.

Astronomers believe that, during the formation of the Solar System, Jupiter’s strong gravitational pull caused nearby planetesimals to smash into one another rather than build up into another planet. This left the belt of fragments we call the asteroids.

The asteroids have continued to collide with one another since their formation, producing smaller fragments called meteoroids. These have occasionally crashed on to Earth’s surface (when they are known as meteorites). It is feared that one day a large meteorite may devastate Earth, causing climatic change sufficient to wipe out many life-forms.

            Most asteroids are rocky, indicating they come from the outer layers of a former minor planet. But some are metallic – they come from the core of such a planet.

            A close-up view of the irregular shaped objects that make up the asteroid belt between Mars and Jupiter. From study of asteroid fragments that have fallen to Earth, scientists have dated the age of the Solar System to 4.6 million years ago.

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What are comets?

COMETS

Comets are potato-shaped lumps of dust measuring only a few kilometres across, but accompanied by (when near the Sun) tails of has or dust that stretch for hundreds of millions of kilometres across space. The lump of dust is fused together by frozen gases and water ice. Like all other objects in the Solar System, comets orbit the Sun, although their orbits are often very elliptical (elongated ovals), looping in towards the Sun from distant reaches of the Solar System. When a comet approaches the Sun, part of its ices melt and the gas and dust escape, forming a surrounding cloud, or coma. As it rounds the Sun, the coma is swept back into two tails, a straight gas tail and a broader, curved dust tail, always pointing away from the Sun.

Sometimes, small pieces of debris break off from comets. Great showers of these fragments, called meteors, sometimes come quite close to Earth. Millions of tiny particles burn up in Earth’s atmosphere. Commonly known as shooting stars, they appear to us as split-second streaks of light in the night sky.

FAMOUS COMETS

The English astronomer Edmund Halley (1656-1742) was the first to realise that comets were orbiting objects. He once made a famous prediction: a comet that he observed in 1682 would return to the skies in 1758. Halley believed that comets recorded in 1531 and 1607 were simply earlier sightings of the one he saw in 1682. Halley did not live to see his prediction come true. Halley’s Comet, as it has been known ever since, was duly sighted on Christmas Day 1758 and has reappeared every 75 to 76 years. When Halley’s Comet appeared in March 1986, the space probe Giotto flew within 600 kilometres of it, sending back pictures and sampling the gases and dust particles given off by it.

A sighting of a comet is always a great event. The 1997 appearance of Comet Hale-Bopp was the most spectacular of recent years. Comets can also be destructive if they pass too close to a planet. In July 1994, drawn in by gravity, fragments of Comet Shoemaker-Levy smashed into Jupiter, creating massive fireballs on impact.

            On 30th June 1908 there was a huge explosion in the Tunguska region of Siberia, Russia. Trees in an area about 100 km across were felled by the blast, but no crater was found. The Tunguska fireball may have been a comet exploding at an altitude of about 6 km.

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Do we have some more Moons also, other than Earth’s natural satellite?

MOONS

Moons, also known as satellites, are relatively small worlds that orbit the planets of the Solar System. Earth has one moon, known simply as the Moon, but other planets have many more – Saturn, for example, has at least 18 moons. Moons are very varied in size and form. Many have unusual landscape features that intrigue astronomers.

Moons are created in different ways. Some are the result of fragments of rock or ice being pulled together by gravity to form a globe. Others are asteroids that have been “captured” by a planet’s gravitational force.

All seven of the moons illustrated here larger than the smallest planet, Pluto, while the largest moons, Ganymede and Titan, are even bigger than Mercury, the second smallest planet. Jupiter’s four largest moons are all in the top seven. They are called the “Galileans” after the Italian scientist Galileo Galilei who first discovered them with one of the first telescopes in 1610. Ganymede has an icy surface with cratered plains and areas showing strange “grooved” patterns.

Titan, Saturn’s largest moon, is the only moon to have a thick atmosphere, made mainly of nitrogen. Beneath its continuous cloud layer, there may be a sea of methane.

Callisto, Jupiter’s second largest moon, is heavily cratered. Measuring 600 kilometres across, its most prominent crater, called Valhalla, is surrounded by a series of ripples. Io, the third of Jupiter’s Galileans, with its crust a vivid mixture of yellows, oranges, reds and blacks, looks a little like a pizza. In fact it is peppered with active volcanoes and lakes of molten rock.

Our own Moon is the fifth largest moon in the Solar System, although it would take 81 Moons to make up a world the size of Earth. The Moon’s lava plains indicate past volcanic activity, but there are no active volcanoes there today.

Next in order of size comes Europa, the fourth Galilean and an object of great interest amongst astronomers. Looking like a cracked egg, its surface consists of ice sheets that are continually melting and re-solidifying. It is by no means impossible that, beneath those ice sheets, there is a warm ocean of liquid water. Could it be that life has also evolved on Europa and that there are life-forms swimming in its oceans? Future space probe missions may find out.

Triton is Neptune’s largest moon. Its surface is the coldest place known in the Solar System. At -235°C, the temperature is low enough to freeze nitrogen. Triton was photographed in stunning detail by Voyager 2, the last of its close encounters, in 1989.

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Will you add some facts about Planet Pluto in my knowledge Bank?

PLUTO

Pluto is the smallest, coldest and outermost planet in the Solar System. It was the last to be discovered, identified in 1930 by the American astronomer Clyde Tombaugh. He compared photographs of part of the sky taken six days apart and noticed that a pinprick of light had moved slightly against the background of stars. Pluto was the only outer planet not visited by Voyager 2, so astronomers still know little about it. Some even propose that Pluto is really a comet and not a planet at all.

Pluto has a very elongated orbit, ranging between 7400 and 4400 million kilometres from the Sun, bringing it inside the orbit of Neptune for part of the journey. Pluto’s moon, Charon, is just over half its size and lies only 19,640 kilometres away from it. Both spin in a direction opposite to that of the other planets except Venus.

Pluto is denser than the icy moons of Uranus and Neptune, suggesting that it has relatively large, rocky core.

Pluto’s surface is probably an “icescape” of frozen nitrogen, carbon monoxide and methane. There may be craters made by collisions with rock and ice fragments. Seen from Pluto, the Sun looks no more than a bright, distant star. It still provides just enough heat to evaporate some of the surface frost and create an extremely thin atmosphere. Charon, Pluto’s nearby moon, features prominently in the sky.

Thousands of icy objects may exist in the outer reaches of the Solar System. They may form either a belt or a cloud. This could be the birthplace of comets.

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Will you add some facts about Planet Neptune in my knowledge Bank?

NEPTUNE

Neptune was discovered by German astronomer Johann Galle in 1846. Its largest moon, Triton, was recorded a few days later. Besides that, very little was known about Neptune until the space probe Voyager 2 visited it in 1989.

A bright blue globe, Neptune almost completely lacks surface features. At the time it was photographed by Voyager, a storm system, called the Great Dark Spot (which later disappeared), could be seen racing in a direction opposite to the planet’s rotation. Winds on Neptune blow at more than 2000 kilometres per hour.

Like the other gas giants, Neptune has a system of rings. There are four extremely faint rings, composed of dark, icy fragments.

VOYAGER 2

The greatest journey by a space probe so far undertaken was made by Voyager 2. Between 1979 and 1989, it flew close by Jupiter, Saturn, Uranus and Neptune, transmitting superbly clear pictures of the planets and their moons. Voyager has since sped away from the Solar System, although it continues to send back signals – 20 billion times weaker than those of a watch battery!

Voyager is playing its part in the search for life in other solar systems. Should aliens ever come across the space probe they will find an audiovisual disc on board. If they play it, they will hear, among other things, the sounds of whales, baby crying and greetings in 55 languages.

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Will you add some facts about Planet Uranus in my knowledge Bank?

URANUS

Uranus was discovered in 1781 by William Herschel, an amateur German astronomer living in England. More recently, astronomers found that Uranus is tilted 98° from the vertical, meaning that it orbits the Sun almost on its side. So for much of the 84-year-long journey, both poles face long periods of continuous daylight, followed by continuous night.

            Uranus’ relatively small, rocky core is surrounded by a slushy ocean of water with some ammonia. Its thick atmosphere is composed mainly of hydrogen.

            Uranus has a family of 11 faint rings, none more than 10 km wide, each made up of pitch-black blocks, measuring only a few metres deep. They circle Uranus’ equator.

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Will you add some facts about Planet Mars in my knowledge Bank?

MARS

Although Mars is much smaller than Earth, the two planets have a number of similarities. The Martian day is only a little longer than ours and its angle of tilt means that Mars has four seasons, just as we do on Earth. Daytime temperatures at the equator in midsummer can sometimes reach 25°C. Thin clouds of water vapour or early morning surface frosts can also sometimes be seen. Like Earth, Mars has volcanoes, mountains, dried-up river beds, canyons, deserts and polar icecaps.

For these reasons, Mars is thought to be the only other planet where life may once have existed. However, analysis of the Martian soil by space probes Viking 1 and 2, which touched down on the planet in 1976, and Pathfinder in 1997, failed to find any sign of past or present life.

Mars is a barren planet. Its reddish colour comes from iron oxide dust (similar to rust). From time to time, large dark regions appear on the surface. These are areas of bare rock, exposed when storms remove the dusty covering. The Martian landscape features some dramatic landforms. The Solar System’s highest mountains and its deepest canyon, Valles Marineris, are found on Mars.

Mars has quite a low density and a very weak magnetic field. This suggests that it has only a relatively small ball of iron at its core.

 A number of valleys and channels have been carved into the Martian plains. From the evidence of sediments – muds and silts deposited by water – it seems likely that there were once rivers, lakes and even seas on Mars. The only water left on the surface today is frozen in the polar icecaps. The rest may have been lost to space due to Mar’s weak gravity, or hidden from view as a deep-frozen layer beneath the surface.

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Will you add some facts about Planet Moon in my knowledge Bank?

MOON

The moon is neither a star nor a planet. It is a ball of rock that travels around Earth, taking about 27 days to complete the circle. It is the brightest object in the night sky, although the light it “shines” is reflected from the Sun.

The Moon may have formed when a large object or planetesimal collided with the newly-formed Earth more than four billion years ago. The impact “splashed” into space vast amounts of debris that later came together to form the Moon.

            A completely barren world, the Moon’s surface consists of cratered highlands and wide plains. The Moon’s internal structure is similar to Earth’s; its crust is thicker and not divided into tectonic plates.

            With neither air nor liquid water, it is impossible for plants or animals to live on the Moon. The barren lunar landscape is pitted with craters, blasted out by meteorites crashing to its surface. Scattered debris has left streaks radiating from some craters. The Moon also has wide, smooth lava plains. Early astronomers thought these were seas. They are still called by the Latin name for sea, mare.

PHASES OF THE MOON

The shape of the Moon appears to change from one night to the next. This happens because, as it travels round Earth, it spins only once, so the same face remains pointed towards us at all times. It is our view of the sunlit part that changes. When the face pointed towards us is turned away from the Sun, we cannot see the Moon at all: a New Moon (1).When it is turned towards the Sun, we see a complete disc: a Full Moon (5). In between, it passes through crescent (2), quarter (3) and gibbous (4) phases, and back again (6-8).

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Will you add some facts about Planet Saturn in my knowledge Bank?

SATURN

All four gas giants have rings, but Saturn’s, visible from Earth through even a small telescope, are broad, bright and magnificent. As detailed photographs taken by Voyager 2 show, the rings are made up of billions of blocks of ice and rock, ranging in size from boulders as large as houses down to tiny fragments the size of snowflakes. They are only a few tens of metres thick. Some astronomers think that the rings are the fragmented remains of a moon that was smashed apart by a passing comet.

Three rings can be made out from Earth. The outer ring (A ring) is separated from the other two lying inside it (B and C) by a gap called the Cassini Division. Voyager 2 spotted fainter rings beyond A ring. It also revealed that each ring was, itself, divided into thousands of ringlets.

Saturn has a large family of moons, many of which are small, irregularly shaped bodies with some even sharing the same orbits.

Swirling clouds and storms can sometimes be seen as ripples on Saturn’s globe. Saturn rotates very quickly, producing a distinct bulge at its equator. It is the least dense of the planets: if a large enough bathtub could be found, Saturn would float in the water!

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Will you add some facts about Planet Jupiter in my knowledge Bank?

JUPITER

Jupiter is the largest planet in the Solar System. Large enough to contain more than 1300 Earths inside it, Jupiter is more massive than all the other planets combined. Along with Saturn, Uranus and Neptune, Jupiter is known as a “gas giant”, because it is mostly made of gas with no solid surface at all.

The colourful patterns of red, brown, yellow and white on Jupiter’s surface are produced by the chemicals sulphur and phosphorus in the swirling atmosphere. Jupiter’s extremely quick rotation is probably responsible both for separating the clouds into different colour “zones” (the lighter bands) and “belts” (the darker bands), and for the continual storms. The Great Red Spot, its most famous feature, is such a storm. The quick rotation also causes Jupiter to bulge at its equator, so that it measures 7500 kilometres less from pole to pole.

Jupiter has a system of rings consisting of dark grains of dust. The four largest of its moons are bigger than the planet Pluto. The beautiful, ever-changing patterns on Jupiter’s globe are violent winds.

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Will you add some facts about Planet Venus in my knowledge Bank?

VENUS

About the same size as Earth, Venus is shrouded in thick, unbroken clouds made of droplets of deadly sulphuric acid. Because its cloud cover reflects the light of the Sun from its surface, Venus is a very bright object in the night sky.

Some 25 kilometres thick, the clouds prevent most sunlight from reaching the surface. But another kind of radiation from the Sun, called infrared, does get though and Venus’s dense atmosphere stops it from escaping. The result is a constant surface temperature hotter than the melting point of lead and the hottest in the Solar System. If any space explorer landed on Venus, he or she would be simultaneously incinerated, suffocated by the unbreathable carbon dioxide air, dissolved by acid and crushed by air pressure about 90 times that on Earth.

Venus spins slowly on its axis, actually taking longer to complete one rotation than to orbit the Sun. Relative to all the other planets except Pluto, it spins backwards.

            Venus is covered by thick clouds. They race round in the planet in just four days. The interior of Venus is similar to that of Earth, although its metallic core is much larger than Earth’s.

            Beneath the clouds, Venus’s barren surface features tens of thousands of volcanoes (some possibly still active) surrounded by vast lava plains. Lava flows have cut channels in the ground that look as if they may have been carved by rivers. Odd, dome-shaped volcanoes, or “pancakes”, as they have been described, have formed where lava has oozed to the surface, and then cooled as it spread out in all directions.

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Will you add some facts about Planet Earth in my knowledge Bank?

EARTH

Our own planet, Earth, is the largest of the four inner planets. Third in order of from the Sun, 71% of its surface is taken up by oceans. Water is also present as droplets or ice particles that make up the clouds, as vapour in the atmosphere and as ice in polar areas or on high mountains.

Liquid water is essential for the existence of life on Earth, the only body in the Solar System where life is known to be present. Earth’s distance from the Sun – neither too close nor too far – produces exactly the right temperature range. The atmosphere traps enough of the Sun’s energy to avoid temperature extremes. It also screens the harmful rays of the Sun and acts as a shield against bombardment by meteoroids.

Earth’s magnetic field is generated by electrical currents produced by the swirling motion of the liquid inner core. The magnetic field protects Earth from the solar wind.

Earth’s outer shell, made up of the rocky crust and partly-molten upper mantle, is divided into about 15 separate pieces, called tectonic plates. Volcanoes and earthquakes occur where plate edges meet.

            When Earth lies directly between the Sun and the Moon it casts its shadow on the Moon. This is called a lunar eclipse.

            In contrast to the barren landscapes of the other planets, much of Earth’s is covered by vegetation, including forest, scrub and grassland. Different climates determine the types of plants and animals that live in different places. Large areas show the important influence of humans: for example, farmland, roads and cities. Land areas are continually sculpted by the weather and moving water or ice.

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Will you add some facts about Mercury in my knowledge Bank?

MERCURY

          Mercury, the closest planet to the Sun, is the second smallest planet in the Solar System. Because it is so near the Sun, it can be seen from Earth only with difficulty – low in the dawn or twilight sky close to the Sun.

          Mercury’s surface looks quite similar to that of our Moon. Bare and rocky, it is covered with craters, the result of continual bombardment by meteorites during the first billion years of its existence. Originally molten, Mercury’s surface shrank as it cooled after the bombardment eased, resulting in “wrinkles” – long mountain chains. With no winds or water to erode the rocks, Mercury’s landscape has remained the same ever since.

           Mercury’s orbit has an unusual shape All the other planets, except Pluto, have nearly circular orbits, but Mercury’s is elliptical – more like an oval. At its closest, Mercury is 46 million kilometres from the Sun, 70 million kilometres away at its most distant.

            Mercury has great extremes of temperature. Where it faces the Sun, it can exceed 400°C, but during the long nights (lasting about 59 Earth days) and with no atmosphere to keep the heat in, temperatures can plummet to – 170°C.

            Mercury’s surface is made up of thousands of craters, as well as mountains and lava plains.

            Mercury, the densest planet apart from Earth, has a large metal core made of iron and nickel, surrounded by a thin rocky shell.

            The landscape of Mercury is dominated by thousands of craters. The huge Sun burns with a fierce heat – turning to severe cold when this face of the planet is turned away from it. Large boulders falling from space have produced craters in Mercury’s surface measuring many kilometres across, some with smaller craters inside. Because there is hardly any atmosphere, Mercury’s skies remain black even during the day.

            When a meteorite strikes the surface of Mercury, it punches a saucer-shaped crater in the ground. Debris is blasted out in all directions, creating long streaks.

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What are Planets?

THE PLANETS

A planet is a large object in orbit around a star. It can be made of rock, metal, liquid, gas, or a combination of these. Planets do not produce light, but reflect the light of their parent star.

In our own Solar System, there are nine planets, including Earth, orbiting the Sun, our parent star. Observations of other stars made by astronomers using powerful telescopes indicate that they, too, have planets. There could therefore be billions of other planets in the Universe.

The Earth is the largest of the four inner, or “terrestrial”, planets: Mercury, Venus, Earth and Mars. They are, as the scale illustration demonstrates, dwarfed by the four “gas giants”, Jupiter, Saturn, Uranus and Neptune, so called because they have comparatively small rocky cores surrounded by thick layers of liquid and gas. Pluto fits into neither category, being a small, outer planet made of ice and rock.

The diagram shows the relative distances of the planets from the Sun. Pacing out their positions would give an even better idea of the huge distances between them. If the Sun were a football, Mercury would be pinhead 10 paces away from it. Earth (the size of a peppercorn) is a further 16 paces on from Mercury, with the Moon a thumb’s length away from Earth. Another 209 paces would bring you to Jupiter (a large marble), while Pluto lies 884 more paces distant. To reach the nearest star, Proxima Centauri, you must walk another 6700 kilometres!

EXPLORING THE PLANETS

Because the giant planets lie so far from Earth, it would take too long for people to travel to them. So space probes have been launched to “fly by” every planet except Pluto and send back pictures. Voyager 2 made the greatest journey. Space probe Cassini visits Saturn in 2004.

THE PLANETS FORM

The Solar System began life as a cloud of gas and dust drifting across the Milky Way Ga1axy. It is thought that a supernova may have sent shock waves racing across space, striking the cloud and somehow causing it to collapse under its own gravity.

Within 100,000 years, the collapsed cloud became a swirling disc, called a solar nebula. Under pressure from gas and dust spiralling inwards, the centre became hotter and denser and began to bulge. It would soon evolve into the infant Sun.

Away from this central furnace, particles of dust began to clump together like snowflakes, first into small fragments of rock, then becoming large boulders. Over millions of years, some grew into blocks several kilometres across, called planetesimals. These eventually started to collide with one another, building up like snowballs to become the four rocky inner planets, Mercury, Venus, Earth and Mars, and the cores of the four gas giants, Jupiter, Saturn, Uranus and Neptune.

The solar wind stripped away any remaining dust and gas, including the atmospheres around the four inner planets. The giant planets lay beyond the solar wind’s fiercest blast, so they were able to hold on to their thick blankets of gas.

Jupiter’s gravitational pull caused nearby planetesimals to destroy one another rather than build up into another planet, leaving a belt of rock fragments, known as asteroids, still orbiting the Sun, as they do today.

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What are constituents of Solar System?

SOLAR SYSTEM

The solar system consists of the Sun and an array of objects that orbit it. These objects include the nine known planets, their 64 known moons, asteroids, comets, meteoroids and huge amounts of gas and dust. The Sun’s great size relative to the other objects in the Solar System gives it the gravitational pull to keep them permanently in orbit around it.

The planets orbit the Sun in the same direction (anticlockwise in this illustration) and in elliptical (oval-shaped) paths. Pluto’s orbit is the most elliptical of all the planets. For part of its journey around the Sun, its orbit actually lies inside that of Neptune. All the planets, and most of their moons, travel on approximately the same plane, with the exception of Mercury and, once again, Pluto, both of which have tilted orbits.

Constantly streaming away from the Sun in all directions is the solar wind, made up of electrically-charged particles (parts of atoms).Travelling at more than 400 kilometres per second, it produces electric currents inside a giant magnetic “bubble” called the heliosphere. The heliosphere protects the Solar System from cosmic rays arriving from space. Its edge, some 18 billion kilometres from the Sun, marks the true boundary of the Solar System.

EARLY ASTRONOMERS

Thousands of years ago, in the time of the ancient civilizations of Egypt and China, people thought that the Sun and Moon were gods, the Earth was flat and the sky was a great dome suspended above it.

In later years, astronomers from ancient Greece proved that the Earth was round. Many believed that the stars were fixed to a great sphere that rotated around the Earth each day. One Greek astronomer, Aristarchus, proposed that the planets, including Earth, orbited the Sun, a star, but most astronomers of this time thought that the Sun, Moon and planets all travelled in circular paths around Earth, the centre of the Universe. Ptolemy, who lived in the 2nd century AD, observed that, while the stars moved across the night sky along regular paths, the planets appeared to “wander” from theirs. He proposed that they each moved in their own small circles, called epicycles, as they orbited Earth.

The Polish priest and astronomer, Nicolaus Copernicus, challenged Ptolemy’s view of the Solar System, declaring that the Sun lay at the centre of a system of orbiting planets. Only the Moon orbited the Earth. Copernicus wrongly believed that the planets’ orbits were perfect circles and that they moved in epicycles. It was left to the German astronomer Johannes Kepler (1571-1630), who showed that the planets moved in elliptical, rather than perfectly circular, orbits. The shapes of their orbits also explained the “wandering” that so perplexed earlier observers, thus disproving the idea that the planets moved in epicycles.

The Italian astronomer Galileo (1564-1642) was the first to use a telescope. From his observations of the moons of Jupiter in orbit around that planet, and the changing shape of Venus as it orbited the Sun, he concluded that Copernicus had been correct: the planets do orbit the Sun.

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Will you give me some I retesting facts about Sun?

THE SUN

The Sun is an ordinary star. To us on Earth it is of crucial importance since no life could exist without it, but it is simply one of billions of stars in the Milky Way Galaxy, itself one of billions of galaxies in the Universe. For a star, the Sun is below average size – some astronomers classify it as a “yellow dwarf”. Yet it is massive when compared to the planets. The Sun contains more than 99 per cent of all the matter in the Solar System. Its diameter of 1,400,000 kilometres is more than 100 times that of Earth.  

The Sun is a spinning ball of intensely hot gas made up almost entirely of hydrogen (three-quarters of its mass) and helium. It produces massive amounts of energy by “burning” about four million tonnes of hydrogen every second.

INTERNAL LAYERS

At the centre of the Sun is the core, a region of incredible pressure (200 billion times that on the Earth’s surface) and intense heat – about 15 million °C. This is the Sun’s nuclear furnace, where the energy that keeps it shining is released. Hydrogen atoms fuse together to form helium. Energy from this reaction flows out from the core through the radiative zone to the convective zone. Here, in a continuous cycle, hot gas bubbles up to the surface before sinking down to be reheated again.

THE SURFACE OF THE SUN

The Sun’s outer shell, the photosphere, is only about 500 kilometres thick and, at 5500°C, much “cooler” than at the core. It is in a state of constant motion, like water in a boiling kettle. Hundreds of thousands of flaming gas jets, called spicules, leap up to 10,000 kilometres into the Sun’s atmosphere, known as the chromosphere.

Invisible lines of magnetic force that twist around the Sun’s globe are the cause of many extraordinary features. Huge arches of fire, called prominences, can be held up above the Sun by magnetism. Flares, sudden, massive explosions of energy, burst forth when the magnetic field shifts. Where magnetic field lines erupt through the photosphere, there are dark, cooler areas (about 4300°C) known as sunspots.

Beyond the chromosphere lies the corona, the Sun’s hot, shimmering outer atmosphere. This is visible from Earth only during a total solar eclipse.

DEATH OF THE SUN

When the Sun’s fuel of hydrogen starts to run out, it will grow into a much bigger and brighter star, called a red giant. It will eventually shed its outer layers into space. All that will remain of the Sun itself will be, at first, a small, extremely dense star (a white dwarf), before it eventually cools and wastes away (a black dwarf).

            By coincidence, the Moon and Sun appear to be the same size in the sky. So when the Moon passes between the Earth and the Sun, it may block out our view of the Sun, a solar eclipse. During a total eclipse, an event only rarely witnessed, the Moon covers the Sun’s surface entirely and the corona shines out from behind a black disc. For a short while, dusk falls. In a partial eclipse, part of the Sun still remains visible.

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What is Constellation?

CONSTELLATIONS

Constellations are areas of the sky, divided up for the purpose of identifying stars, galaxies and other objects in the heavens. Years ago, before telescopes were invented; early astronomers grouped the stars together into patterns, imagining their shapes to look like gods, heroes and sacred beasts from popular legends. The 88 constellations that exist today include 48 known to the ancient Greeks, who inherited some from the Babylonians.

            A line running from two stars in the constellation Ursa Major (great Bear) points to the Pole Star, almost exactly due north. Years ago, seafarers used this observation for navigation.

            Orion, a hunter in Greek myths is an easy constellation to spot. Three stars in a diagonal line form his belt, while others make up his dagger and shield. The belt stars point down towards Sirius, the brightest star in the night sky. In Greek myths, Centaurus was half man, half horse.

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What are Quasars?

QUASARS

Incredibly powerful, massive black holes may, astronomers think, be found lurking at the centres of galaxies. There could even be one at the centre of our own Milky Way Galaxy. Astronomers have detected a ring of fast-moving, hot gas swirling around the centre. The ring of gas is probably in the grip of a powerful gravitational pull – most likely, astronomer’s suspect, to be the work of a black hole.

The activity at the centre of our Galaxy is as nothing compared to that of quasars. These objects look like stars, but they lie at incredible distances from us: the farthest quasars are 13 billion light years away. To be visible at that distance means they must be giving off immense amounts of energy. Quasars are the centres of extremely violent galaxies containing super-massive black holes, weighing up to 100 billion Suns. The brilliant light comes from the disc of hot gas and dust spiralling into the black hole.

            Black holes are invisible, but it is possible to detect them by studying their effects, astronomers observing a star called Cygnus X-1 saw that it was giving off enormous amounts of energy (a sure sign of violent activity in the Universe). They discovered that this huge, hot blue star was being dragged around in a circle by an unseen object with a huge gravitational pull. That unseen object, astronomers now believe, is a black hole, which is tearing gas from the star. The gas forms a whirling disc before plummeting into the black hole. As it falls, it travels faster and faster until it moves almost at the speed of light itself. Close to the hole, the gas becomes so hot it emits massive amounts of energy.

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Why Black Hole is called so?

BLACK HOLES

Black holes are the strangest objects in the Universe. No-one has ever seen one, but most astronomers are convinced that they exist. They are tiny regions of space surrounded by a force of gravity so strong that nothing, not even light, can escape from them.

All bodies in space exert a force of gravity, the force which attracts other things towards them. The greater an object, the stronger it’s gravitational pull, and the harder it is to escape from it. A rocket launched from Earth must go faster than 40,000 kilometres per hour (its “escape velocity”) to escape Earth’s gravitational pull. The Sun is many thousands of times more massive than Earth, so a rocket would have to travel much faster: more than 2 million kilometres per hour. If there was an object much bigger or denser than the Sun, an escape velocity equal to that of the speed of light may be needed to escape from it.

Where might an object of such high density be found? Stars more than 10 times as heavy as the Sun burn up their fuel in a much shorter time – a few million years, compared to the Sun’s 10 billion years. They swell into massive super giants before blasting apart in supernovas. A supernova’s core compresses in seconds to a tiny, super-dense body called a neutron star. If it weighs more than the three Suns, it squeezes further. An escape velocity of the speed of light would be needed to travel away from it. Any light rays would be pulled back in, so the object is invisible: a black hole.

Imagine a star in space as ball on a rubber sheet. A massive object like a star will “bend” space and anything close to it will fall in towards it. If the ball were so heavy that the sheet stretched into a long, deep tube, the result would be a black hole.

EINSTEIN’S GENERAL THEORY

The great German physicist Albert Einstein (1879-1955) found another way to explain how space, light and matter would behave close to a black hole. In his General Theory of Relativity of 1915, Einstein proposed that the gravitational pull of an object would result in the “curving” of space, in the same way that a person can curve a trampoline. A massive object creates a large “dent” in space into which light and matter would fall. The denser the object, the greater the dent. So the Sun would make only a shallow dent, whereas a neutron star would create a very deep dent. A black hole, the densest object of all, creates a dent so deep that nothing can escape from it.

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What are stars?

STARS

Stars are giant spinning balls of hot gases. Like massive nuclear power stations, they produce vast amounts of energy in the form of heat and light, which they radiate across space as they shine.

They may look like tiny points of light in the night sky, but many stars are incredibly big. Betelgeuse, in the constellation of Orion, is 800 times the size of the Sun, our local star. Stars vary enormously according to the amount of light they emit. Some of the most powerful give off more than 100,000 the light of the Sun, while others are 100,000 times weaker.

Stars are born when clouds of dust and gas in space, known as nebulae, compress together under the force of gravity to become dense “blobs”, called protostars. It is not certain why this happens. Maybe the pressure of an exploding star nearby at the end of its life triggers the process.

After a star has formed it becomes a stable “main sequence” star. The Sun is a typical star of average brightness. More massive stars, like Rigel (also in Orion), glow blue-white, while at the other end of the scale, a white dwarf, the collapsed core of an old star, is no bigger than the Earth.

A star begins its life as a dense mass of gas and dust called a protostar (1). The core becomes so hot that nuclear reactions start deep inside it. Gas and dust are blown away (2), although some remain in a disc surrounding the new star. Planets may form here (3). The star is now a main sequence star (4). When the fuel it uses to produce energy runs out, the core collapses and the star swells into a red giant (5). A massive star will become a supergiant that will blast apart in a mighty explosion called a supernova (6). It ends its days as a neutron star or a black hole (7). A red giant will puff away into space, leaving behind a white dwarf.

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What is Galaxy?

GALAXIES

           Galaxies are gigantic collections of stars. The galaxy in which the Sun is situated, the Milky Way Galaxy, is a vast spiral of about 200 billion stars measuring about 100,000 light years across. There are billions more galaxies in the Universe, most of which are elliptical (oval) in shape. There are also others that have irregular shapes.

            The Milky Way has a bulge at its centre, the nucleus, where older red stars are concentrated. Four giant arms radiate out from the nucleus. These contain younger blue stars as well as areas of gas and dust – the raw material for the creation of new stars. The whole spiral spins at a speed of about 250 kilometres per second.

            The Milky Way Galaxy closely resembles the Andromeda Galaxy, which lies 2.25 million light years away. The Sun is situated on one of the spiral arms about halfway out from the nucleus. Here are mostly yellow and orange young-to-middle aged stars.

            The Horsehead Nebula is really a gigantic cloud of dust and gas that has taken on a familiar shape. It is one of many clouds in our Galaxy where stars start to form.

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What is Big Bang Theory?

BIG BANG

Many astronomers believe that the Universe began life in a single momentous event. This was an incredibly hot, dense explosion called the Big Bang, which took place about 15 billion years ago. During this explosion, all matter, energy, space – and time itself – were created.

In the first few millionths of a second, the particles that make up atoms, the building blocks of all matter, were formed. It took about 100,000 years for the first atoms, those of the gases hydrogen and helium, to come together. By this time, the searing heat of the Big Bang had cooled, space had expanded and the gases began to spread out. Gradually, however, gravity drew the gases together, leaving vast regions of empty space in between.

About a billion years after the Big Bang, the clouds of gas started to form into galaxies. Matter inside the galaxies went on clumping together until stars were created. Our own Sun was born in this way about 5 billion years ago. Its family of planets, including our Earth, was formed from the debris spinning round the infant Sun. With billions and billions of stars and planets forming in the same way across the Universe, it seems almost certain that life will have also evolved elsewhere. Will we on Earth one day make contact with these alien life-forms?

The expansion of the Universe is slowing down. Some astronomers think that gravity may eventually bring the expansion to a halt, then collapse all matter once more to a single point in a “Big Crunch”. Others believe that there is not enough material in the Universe to do this and that the Universe will carry on expanding forever.

Many scientists think that all matter in the Universe will eventually collide: the “Big Crunch”. Vast amounts of invisible “dark matter” in the Universe may exert sufficient gravity to halt its expansion and cause the galaxies to compress together.

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What is Universe?

UNIVERSE

Everything that we can think of and everything else that exists – all belong to the Universe. From grains of sand to tall buildings, from particles of dust to giant stars and planets, from microscopic bacteria to people – all are part of the Universe. It even includes empty space.

The Universe is unimaginably vast: billions upon billions of kilometres wide. Distances in the Universe are so great that we have to use a special measure to record them. This is a light year, or the distance that light, which moves at a speed of about 300,000 kilometres per second, travels in one year: about 9,460,528,405,000 kilometres. The nearest star to Earth (after the Sun), Proxima Centauri, is 4.2 light years away. The most distant objects we know in the Universe are more than 13 billion light years away from Earth.

Nearly all the matter in the Universe is contained in galaxies, enormous masses of stars, has and dust. There may be about 100 billion galaxies, each containing hundreds of billions of stars. Galaxies are grouped into giant “clouds” of galaxies, called superclusters. These are spread round the Universe like a net, made up of strings and knots. In between there are gigantic empty spaces.

The superclusters are, themselves, made up of smaller clusters of galaxies. One of these, a cluster of 30 galaxies or so, is called the Local Group. It contains the Milky Way Galaxy, the vast spiral of stars to which our own local star, the Sun, belongs.

Astronomers have discovered that all galaxies are rushing away from one another. This means that, a long time ago, they were once all close together. So the Universe had a definite beginning – and may have an end.

The Universe is composed of many galaxy superclusters, themselves made up of clusters of galaxies. One of these contains the Milky Way Galaxy, a spiral-shaped mass of about 200 billion stars, one of which is our own Sun, parent to a family of nine planets.

The third planet from the Sun is Earth, orbited by the Moon. Earth is the only world in the Universe where life is known to exist, but we may discover others one day.

It is possible that the Universe will carry on expanding forever. In this sequence, the Universe is created in an immense explosion called the Big Bang. It expands rapidly, with all the galaxies moving away from one another as the Universe inflates like a balloon.

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What should I know about Magnetism?

MAGNETISM

We cannot see or feel the force of magnetism. But it is all around us since the Earth is itself a giant magnet. A magnetic force affects mainly objects and substances that contain the metal iron. It pulls or attracts them. The force is present as a magnetic field around a magnet, which is itself usually made of iron.

Magnets of different sizes and shapes have hundreds of uses, from holding notes on a refrigerator to being vital parts in electrical generators, motors and loudspeakers.

A magnet does not always attract another magnet. Its magnetic force is strongest at two areas called its poles. These are different from each other and known as north and south poles. The north pole of one magnet attracts the south pole of another magnet. But it pushes away or repels the other magnet’s North Pole. The general rule is that unlike poles attract, like poles repel.

            A bar magnet is a strip of iron or steel in which the atoms are lined up in a certain way. Its magnetic force is strongest at its two ends or poles.

            The Earth has a magnetic field and two magnetic poles, north and south, almost as if it had a giant bar magnet inside.

            A magnetic compass is a needle-shaped magnet. Its poles are attracted to the Earth’s poles so it always turns to point north-south.

ELECTROMAGNETISM

Electricity and magnetism are two aspects of the same force, called the electromagnetic force. They are so closely linked that one can produce the other. A magnetic field moving near a wire causes electricity to flow in the wire. An electric current flowing in a wire makes a magnetic field around the wire. Twist the wire into a coil and it produces a stronger magnetic field. It can be turned on and off by switching the electricity on and off. This is an electromagnet. Electromagnetism is the basis of electric motors and generators.

            A maglev (magnetic levitation) train uses the pushing force between the like poles of magnets in the train and track. The force holds the wheel-less train above the track.

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Define Light and explain its main features?

LIGHT

Light is a kind of energy. It is the form of energy that our eyes can detect, enabling us to see. It is produced by very hot things – the Sun, fire and the tiny wire inside electric light-bulbs. Certain animals also have light-producing organs.

Light from the Sun is essential to life on Earth. Some creatures live off minerals in the ocean depths but these are exceptions. Most plants use sunlight to make their food. All plant-eating animals, together with other animals that eat plant-eaters, also therefore depend on sunlight.

Light rays can only travel in straight lines. If they strike an object which does not allow light to pass through it (an opaque object), a shadow is cast on the unlit side. Light can be reflected, however. Light reflected from objects allows us to see them. Light rays strike and bounce off a flat, shiny surface like a mirror at the same angle. This enables us to see our reflection.

THE SPEED OF LIGHT

When we switch on an electric light, it seems that the room is filled with light instantaneously. But light rays do take time to travel from their source. They travel extremely quickly: about 300,000 kilometres (or seven-and-a-half times around the world) per second in outer space. The speed of light is, in fact, the speed limit for the Universe: nothing can travel faster. Light waves are able to travel through empty space – a vacuum – whereas sound waves cannot. Light actually moves less quickly through air, water or glass than through empty space.

Because stars are very far from Earth – at least thousands of billions of kilometres – astronomers measure their distances in light years, the amount of time it takes for light to travel to us from them.

REFRACTION OF LIGHT

Light rays bend, or refract, when they pass through different transparent materials. This is because light travels at different speeds through different materials. At the boundary between two materials, for example, air and water, the light changes speed slightly and is refracted from its straight path. You can see this effect when looking at the bottom of swimming pool. It looks much shallower than it really is.

FOCUSING LIGHT

A lens, a shaped piece of glass or plastic, can bend light, either spreading it out or bringing it closer together. A convex lens, one that is thicker in the middle than at the edge, brings light rays together at a single point called a focus. The eye contains a natural convex lens which focuses an image on to the retina at the back of the eye. If you hold a convex lens so that the object you are looking at lies between the lens and the focus, the object will appear larger and further from the lens than it really is. A simple magnifying glass is a convex lens, and is useful for studying minute detail as, for example, on a postage stamp or a tiny insect or flower.

A concave lens is the opposite of a convex lens: it is thicker around the edge than in the middle. This kind of lens diverges (spreads out) light rays. It is used in glasses to correct short-sightedness.

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What should I know about Electricity?

 

ELECTRICITY

One of the most useful forms of energy in today’s world is electricity. It is transportable, which means it can be carried long distances by wires and cables. It is convertible, being changed into many other forms of energy, such as light from an electric light-bulb, and movement in an electric motor. It is also controllable. We can turn it on and off with a switch, or up and down with a knob. When a city suffers a power cut and falls still and silent, we realize how much we depend on electricity.

Electricity is the movement of electrons, the negative particles around the nucleus of an atom. Most metals, especially silver and copper, have electrons that can move easily from atom to atom, so they are good carriers or conductors of electricity. Electrons are pushed along the conductor by a battery or generator. But they flow only if they have a complete pathway of conductors called a circuit. Flowing electricity is known as electric current.

In substances such as rocks, wood, plastics, rubber and glass the electrons do not move easily. These materials prevent the flow of electricity and are known as insulators, but they may gain or lose electrons on their surface as a static electric charge.

            Static electricity is produced when electrons are separated from their atoms. On a comb it attracts bits of paper. In the sky it causes lightning!

            Electric current flows along a wire as electrons which detach from the outermost parts of their own atoms and jump or hop along to the next available atoms.

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Could you please tell something interesting about Colours and World of Colours?

COLOUR

One of the main features of light is colour. If light were just pure white, our whole world would be black and white and shades of grey. But white light is not pure. It is a mixture of all the colours of the rainbow which are known as the spectrum of light.

Colours exist because light is in the form of waves and not all the waves have the same wavelength. Some are slightly longer than others, and these we see as red. Light waves of medium wavelength appear to our eyes as green. We see the shortest light waves as violet. A leaf is green because its surface absorbs all the colours in white light except green, which it reflects into our eyes. A red flag absorbs all colours except red. Objects that reflect all colours are white.

The colour wheel shows how the different colours of light add up to make white light. When you spin the wheel the colours whirl around so fast that the eye cannot follow them. Inside the eye each colour merges with the others so the eye sees all the colours at once – and all colours of light added together make white light.

The different colours of light are seen when white light is split up using a prism, an angled block of transparent material such as clear glass or plastic. As the light waves pass into and then out of the prism they are bent or refracted. Longer waves of red light refract least. Shorter waves of violet light refract most. The other colours spread out between. A raindrop works as a natural prism. Millions of raindrops split sunlight and form a rainbow in the sky.

ADDING COLOURS

We see colours in books and on screens such as the television, in different ways. A television or computer screen has thousands of tiny dots that glow and give out light. These dots have actually only three colours – red, green and blue. These colours are known as the primary colours of light. Added to each other in different combinations and brightness they can make any other colour. For example, red and green together make the colour yellow. Red and blue produce the pinky colour known as magenta. Blue and green form cyan, a type of turquoise. The three primary colours of red, blue and green added together make white light.

On the screen of a computer or TV the dots are arranged in groups known as pixels. The different colours of dots flash on and off in different combinations and shine with different brightnesses. From a distance, the eye cannot see the individual dots. They merge to produce larger areas of colour. When all the red dots on an area of the screen shine, that area looks red. When all three colours of dots in an area of the screen shine brightly, that area looks white. Also the dots flash on and off many times each second, again too fast for the eye to follow. So they merge together in time to produce multi-coloured, moving pictures.

SUBTRACTING COLOURS

Coloured pictures in a book are made like those on a screen, using tiny coloured dots that merge together. The dots are inks made with coloured substances called pigments. There are three primary pigment colours – yellow, magenta and cyan. They work in the opposite way to light colours. They do not add together, but take away or subtract. A yellow dot takes away all colours of light except yellow which it reflects. The other two dots do the same for their colours. By taking away individual colours, the dots merge to produce areas of other colours. All three dots together make black.

            The wolf’s mask is realistic and frightening. Yet it is printed using tiny dots of only three colours. They can be separated as magenta, cyan and yellow. To save on coloured inks some parts of the page, like these words, are printed with ready-made black ink.

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How does Transfer of Heat take Place?

HEAT MOVES

Heat can move around and between objects in three main ways. One is conduction, when heat energy passes between two objects in physical contact. When you touch an object to see how warm it is, you receive some of its heat by conduction. A second way is by convection. This only happens in liquids and gases. As some of the atoms or molecules receive heat energy and become warm they spread out more. The heated part of the liquid or solid is now less dense than its cooler surroundings so it rises or floats. As it rises, it carries its heat energy in the form of convection current. You can feel this as warm air rising from a central heating radiator.

The third way that heat moves is by radiation. It is in the form of infrared waves which are part of a whole range of waves, including radio waves, light and X-rays, known as the electromagnetic spectrum. Conduction and convection both need matter to transfer heat. Radiation does not. Infrared waves can pass through space, which is how the Sun’s heat reaches Earth.

Like light waves, infrared waves reflect from light-coloured or shiny surfaces. On a hot day, light-coloured clothes reflect the Sun’s warmth and keep you cooler than dark clothing, which absorbs the warmth. Substances that slow down conduction and convection, such as wood, plastic and glass fibre, are called thermal insulators. Layers of fat, or blubber in a whale, are good insulators.

The faster an aircraft goes, the greater the heat from friction with air. Very fast planes like the X-15 rocket have special heat-radiating paint that gives out heat as fast as possible, to prevent the metal skin of the plane melting at high speed.

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How would you distinguish between Pitch and Volume of Sound?

PITCH AND VOLUME

Sound has two important features. One is pitch. A low-pitched sound is deep, like a roll of thunder or a booming big drum. A high-pitched sound is shrill, like a snake’s hiss or the tinkle of a triangle. Pitch depends on the frequency of sound waves – the number of waves per second. High-pitched sounds have high frequencies.

Some sounds are so high-pitched that our ears cannot detect them. They are known as ultrasounds. Many animals, like dogs and bats, can hear ultrasounds.

The second important feature of sound is its loudness or volume. Some sounds are so quiet that we can only just hear them, like a ticking watch or the rustling of leaves. Other sounds are so loud, like the roar of engines or the powerful music in a disco, that they may damage the ears. Sound volume, or intensity, is measured in units called decibels (dB). Sounds of more than 80-90 decibels can damage our hearing.

            An ultrasound scanner beams very high-pitched sound waves into the body. The echoes are analyzed by a computer to form an image, the baby in the womb.

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How would you explain Heat?

HEAT

How warm is the weather today? It may be cold and wintry or hot and summery. Heat is a vital part of our lives. We need to keep our bodies comfortably warm with clothing, especially in cold conditions. If body temperature falls from its normal 37°C to below about 30°C, fatal hypothermia may set in.

We cook our food with heat using gas or electricity. Countless machines and industrial processes use heat, from making pottery or a photocopy to a steelworks or power station. Heat is also given off as a waste form of energy by many processes. In a power station most of the heat is used to generate electricity, but some is released as clouds of steam from huge cooling towers.

Heat is a type of energy – the vibrations of atoms and molecules. The more an atom moves or vibrates, the more heat or thermal energy it has. In a solid, the atoms have fixed central positions but each atom vibrates slightly about its central position, like a ball tied to a nail by elastic. Heat the solid and the atoms vibrate more. When they have enough vibrations, the atoms break from their fixed positions (the “elastic” snaps), and they move about at random. The solid has melted into a liquid. Heat it more and the atoms fly further apart. The liquid becomes a gas.

 TEMPERATURE

Cold is not the presence of something that opposes heat, but simply the lack of heat. Temperature is not the same as heat. Heat is a form of energy, while temperature is a measure of how much heat energy a substance or object contains. A slice of apple pie at 40°C contains more heat energy than a same-sized slice of the same pie at 30°C. We can judge its temperature quite accurately when we touch the slice with our skin, and especially with our fingertips or lips. But this judgement is only safe within a certain range. Temperatures greater than about 50°C or lower than about -10°C cause pain and may damage the skin. We measure temperatures accurately using devices called thermometers.

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What do you know about Sound?

SOUND

One of the most familiar forms of energy in daily life is sound. We hear natural sounds like birdsong and wind. We hear the noise of vehicles and machines, and sounds such as speech and music from radios, televisions and stereo systems. We also rely on sounds to communicate when we talk to others.

Sounds are made by objects that vibrate (move to and fro rapidly). As an object vibrates, it alternately pushes and pulls at the air around it. The air is squashed and stretched as the molecules of the gases in air are pressed close together and then pulled farther apart. These are regions of high and low air pressure. They pass outwards away from the object in all directions. They are called sound waves.

Sound waves start as the energy of movement in the vibrations. This is transferred to the energy of movement in air molecules. As the sound waves spread out they widen and disperse, like the ripples on a pond after a stone is thrown in. So the sound gradually gets weaker and fades away. However if there is a hard, smooth surface in the way, such as a wall, then some sound waves bounce off it and come back again. The bouncing is known as reflection and we hear the returning sound as an echo.

Sounds also travel as vibrations through liquids, such as water, and solids, such as metals. The atoms or molecules are closer together in liquids than in air, and even closer still in solids. So sounds travel through them much faster.

            An object that vibrates to produce sound waves is a sound source. A bow rubs over the cello’s string and makes it vibrate. The vibrations pass into the air and also to the cello’s hollow body making the sound louder and richer.

The speed of sound varies depending on the substance it travels through. Atoms in steel are closer than molecules in air, so the vibrations of sound move faster and further.

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What is Conservative Energy?

CONSERVING ENERGY

Energy can be changed or converted from one form to another. But it is never destroyed or created, lost or gained. It is conserved – the amount stays the same. At the end of a process or event, the total amount of energy is the same as at the beginning. For example, the chemical energy in a car’s petrol is converted into the same amount of energy as the car’s motion, heat and sound. The principle of energy conservation means the total amount of energy in the Universe is always the same.

Another form of energy is matter itself. Matter can be converted into energy and energy can be changed into matter. This conversion is used in nuclear power stations. A nuclear particle called a neutron smashes into the nucleus of a uranium atom (1). The nucleus breaks into two parts (2). This releases large amounts of heat and other energy and also two more fast-moving neutrons (3). These smash into more uranium nuclei and so on in a chain reaction (4). Splitting of nuclei is known as nuclear fission. During the process bits of matter cease to exist and become vast quantities of energy instead.

A similar process of changing matter into energy happens naturally in the Sun. The Sun is made mainly of hydrogen. Tremendous temperatures and pressures at its centre squeeze or fuse together the nuclei of the atoms (1) to form the nucleus of a helium atom (2).Vast amounts of energy are given off (3) which emerge from the Sun mainly as light and heat. A neutron may also be given off to continue the reaction (4). Since the nuclei join or fuse, this is called nuclear fusion. Compared to fission used in our nuclear power stations, fusion power would cause less radioactive wastes and pollution. Fusion power may be the energy source of the future.

            Geothermal energy from hot rocks deep in the Earth causes geysers, jets of hot water and steam. This form of energy will last millions of years.

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What do you mean by Energy?

ENERGY

Energy is the ability to make things happen, cause changes and carry out work. Any change anywhere in the Universe, from a tiny meteorite hitting a planet to an exploding star, means that energy is at work. In daily life, energy is all around us in many different forms. Light and sound energy travel through the air as waves. Heat is a form known as thermal energy. Movement or motion is, too, and is called kinetic energy. Objects even have energy because of their place or position. This is called potential energy. A boulder on a hilltop has potential energy because gravity tries to pull it down. As the boulder begins to roll its potential energy changes into kinetic energy.

Energy can cause changes and it can change itself. It can convert between one form and another. The boulder rolls down the hill, converting some of its potential energy to kinetic energy. Water also flows downhill with kinetic energy. We can harness this kinetic energy in a hydro-electric power station and convert it into electrical energy, yet another form of energy. Electricity is very useful in our modern world. It can be transported long distances along wires. It can be converted to other forms of energy, like light from a light bulb, heat in an electric kettle and sound from a loudspeaker.

Matter contains chemical energy, in the links or bonds between atoms. The bonds need energy to form and they release this energy when they are broken. We make use of chemical energy in fuels such as petrol. The bonds break as the fuel burns and releases heat.

Energy from the Sun bathes our world. It is in two main forms, light and heat. It takes more than 8 minutes to travel nearly 150 million kilometres through space to Earth.

Energy is all around, present in different forms and changing from one form to another. Without energy our world would be completely dark, cold, still and silent.

The human body needs energy to drive its life processes like heartbeat, breathing and movement. The energy is present in chemical form as the nutrients in our food. We digest the food to obtain the energy and store it as body starches and sugars.

Chemical energy in the body in the form of blood sugar is taken to muscles. The muscles convert it into the energy of motion so we can move about.

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How do trawlers fish?

               There is perhaps no human activity older, more varied or stranger, than fishing. He tricks and catches fish in different ways, such as using his bare hand, or fishing even with harpoon guns in whaling! But the method most used today is the one by which it produces the biggest share of commercial fishing known as trawling. Do you know how do trawlers fish?

               Trawlers fish with a bag-size net. It is let out on long warps or ropes. The fish are swept in at the wide, open end and then get trapped at the narrower, closed end. The trawler may be between 100 to 1500 metres long or more. In this system, the motorized fishing boats trawl by towing a large net in three different ways to keep the mouth of the net open. Firstly, a beam can be placed across the head of the net; secondly a pair of boats can be used – one at each side of the net to tow it and thirdly, some floating weights, called otter boards can be attached to the sides of the mouth of the net.

               However, the beam trawl is only used on a few small fishing crafts, and on the other hand, pair trawling is used to catch fishes from the bottom of the sea to enormous depths, sometimes at the range of 1500 metres or more. When the net is full, powered winches haul it on the board through a ramp. The otter trawl is widely used and is employed on almost every fishing technique except the smaller trawlers.

               The net gathers in everything including eggs, newly hatched fishes and algae. But this system is considered to be very destructive and alarming in the context of overfishing along the seas. Sometimes an entire fleet of fishing vessels is headed by a large factory ship fitted out just for processing of the catch. A single “sweep” of the net often taken in terms of tonnes of fish provides an idea of the quantity of fish caught in rich seas. Deep sea fishes like sardines and herrings together account for eighteen percent of the world’s catch.

               Today, the large motor fishing vessels are fitted with sonar or echo-sound equipments to locate a shoal of fish.

 

Where would a ball fall when thrown inside a running train?

               You might say that the ball would fall behind the person who throws it because he would have moved forward with the moving train. But in fact this is not correct.

               You can perform a simple experiment to answer this question. You would be surprised to find that the ball lands right in your hand when thrown upward inside the moving train. Do you know why it happens so?

               In a moving train everything inside the train also moves with the speed of the train, for example, the fans, passengers, you and the ball in your hand. When you throw up the ball, a part of the speed of the train is imparted to it. It acquires a vertical motion in addition to its horizontal motion. The passengers in the train cannot see its horizontal motion but only its upward and downward movements.

               Imagine a man outside the train, who is watching your experiment. As we have said the ball possesses both vertical and horizontal motions, both these motions combined together make the ball travel along a parabolic path. The observer outside the train will see the ball moving in a parabolic path but a passenger in the train will see only the up and down motions of the ball.

               Now the question arises whether the ball follows the parabolic path or just moves up and down? Out of these two which one is right? In fact, all motion is relative to the observer. There is nothing like absolute motion and hence the motion of the ball is different for the two observers. 

How does an Electric Bell function?

               When you push the button of an electric door bell or calling bell it keeps on ringing as long as the button remains pressed.

               Do you know how does it function? An electric bell is a simple device based on the magnetic effects of electric current. It is used in offices, houses, industries and for fire alarms.

               It consists of a U-shaped electromagnet and a soft-iron armature. The armature has a small hammer for striking the gong. This hammer hits the gong repeatedly and produces sound. The gong is made of a metal. For operating the bell, a push button is pressed. In an electric bell, the button is a switch that connects the supply of electricity to the bell.

               When the button of the bell is pressed, the current flows through electromagnet winding, armature, contact spring and the contact screw. The flow of the current magnetizes the soft-iron core of the electromagnet. This attracts the armature, causing the attached hammer to strike the metal gong and thereby produce sound.

               As the armature moves forward due to magnetic attraction the contact spring moves away from the contact screw. This breaks the circuit and the current stops flowing. As a result, the soft-iron core loses its magnetism. It, therefore, no longer attracts the armature which, then, is pulled back by the contact spring to its original position. As soon as the armature comes to its original position the electric circuit is again completed and the soft iron becomes magnetized. It again attracts the armature and thereby the hammer strikes against the gong and produces sound. As long as the push button remains pressed, the circuit is alternately broken and completed causing the hammer to strike the gong. Thus an electric bell keeps ringing.

               If a steel core is used instead of a soft-iron, then the steel core will become a permanent magnet due to passage of electric current through the winding. Consequently, the armature will stay attracted even when the contact spring moves away from the contact screw, so the hammer will strike the gong only once.

 

What is Osmosis?

               It is a well known fact that when resins are put in water they get swollen. This swelling takes place due to the entry of water through the membrane of the resins. Similarly, if grapes are put in sugar solution they shrink. Swelling of resins and shrinking of grapes take place due to a process known as osmosis. Do you know what this osmosis is?

               Osmosis is a process in which a solution of lower concentration passes into a solution of higher concentration through a semipermeable membrane. A semipermeable membrane is one that allows some, but not all, substances to pass through it. This contains very small pores. When resins are put into water, the covering acts as a semipermeable membrane. Water is less concentrated than the substance present inside the resins and so the water moves into the resins through its semipermeable membrane. Similarly, fluid from grapes moves out through the semipermeable membrane, as the concentration of sugar solution is more than that of the grapes. There is a tendency for solutions separated by a membrane to become equal in molecular concentration.

               In osmosis, the movement is always from a dilute solution into a solution of higher concentration. This reduces the concentration of the stronger solution. The rate of osmosis depends upon the comparative strengths of the two solutions. The greater the difference, the faster the rate of osmosis. This process continues until both solutions are of equal strength. When this equilibrium is reached, osmosis stops.

               Osmosis is an ongoing process among the living beings. The membranes of cells are semipermeable. Plants absorb water and dissolved minerals from the soil by osmosis; they use osmosis to move the water and dissolved minerals through the plant, cell by cell. Osmosis also maintains turgor pressure. Turgor pressure is the pressure of water on the cell. It gives the cell form and strength. When there is a decrease in turgor pressure, the plant will soon wilt and lose its regular stiffness.

               Osmosis allows the transfer of water and dissolved nutrients in the human body from the blood into the cells.

 

How do electrically heated appliances work?

Electric heaters, immersion heaters, electric irons, electric kettles, etc. are appliances which produce heat through electricity. All these appliances are based on the heating effects of electric current. When electric current is passed through a wire, it gets heated up. Heating of a wire depends upon two facts: first, on the resistance of the wire and then on the amount of electric current passed. The heat produced in the wire is directly proportional to the resistance of the wire and that of the square of the current. The amount of heat produced also depends upon the time for which the current passes through the wire.

Based upon this property of current, many domestic electric appliances have been developed. The working principle of all these appliances is almost the same, the difference lies only in their construction. An electric heater consists of a coil of nichrome wire which is in the form of a spring. This coil is mounted on an insulating base plate made of clay. When electric current is passed through the coil, it gets heated up. Room heaters are also made in a similar way, the only difference being that nichrome wire is wound around an insulating rod and a reflector is mounted at the back of the coil which reflects the heat radiation.

Immersion heaters also consist of a nichrome wire which is enclosed in a metal tube. To isolate the wire from the metal tube, an insulating powder is filled in the tube. This powder acts as an insulator for electricity but conducts heat. When the two terminals of the wire are connected to an electric source, the current starts flowing through the wire and it gets heated up. The immersion heater is put inside a bucket full of water to heat the water.

An electric iron is used to remove the wrinkles from washed clothes. This appliance also consists of a ribbon of nichrome wire which is enclosed between two sheets of mica. This spreads the heat uniformally along the base plate of an electric iron. Mica sheets are mounted on a heavy metal plate. This metal plate, when pressed against the surface of the cloth, removes the wrinkles from the cloth.

Electric irons are of two types: automatic and manual. Automatic one is fitted with a thermostat control which regulates the temperature. Manual irons do not have such a device. When the iron is cold, thermostat provides and maintains a constant temperature by the use of a device that cuts off the supply of heat when the required temperature is exceeded.

An electric kettle is used to prepare tea or coffee. It also consists of a heating element fitted at the bottom of the vessel and is isolated from it. Water is put into the vessel which gets heated when current is passed through the heating element.

For all electrically heated appliances, it is very essential to have an earth connection. Immersion heaters should not be switched on, until there is water in the bucket. The electric bulb is also a similar device whose filament gets heated up when the electric current is passed through it and it produces light.

 

How do a mixer and grinder work?

               Mixer and grinder are very useful domestic appliances. With the help of these appliances we can grate, grind and prepare mango shake, milk shake, cold coffee etc. in a short period of time. Butter can be extracted from cream by using this apparatus. Pulses and spices can also be ground easily with its help.

               This apparatus consists mainly of two parts. One is the base of the apparatus which is fitted with a high speed motor. This motor makes 15-20 thousand revolutions per minute. It also consists of a variable switch by which the speed of the motor can be adjusted with the other part of the apparatus known as a mixer and grinder. This is usually made of stainless steel or plastic in the shape of a jar. It is fitted with blades which revolve with the speed of the motor. This rotating blade minces the food material into small pieces.

               Modern mixer and grinders also consist of other attachments such as a juicer with the help of which we can extract the juices of apples, oranges, tomatoes and other fruits and vegetables. In this attachment juice pours out on one side and pulp from the other side. Most modern grinders and mixers can be fitted with various other attachments such as a slice grater, meat mincer, dough maker etc. Nowadays we have grinders by which even wheat or maize can be ground.

               These electrically operated machines have minimized the tedious work in a kitchen. Not only do these machines save time but also provide neat, clean and tasty food for us. Moreover, these machines do not consume much electricity.

What is a Robot?

          A robot is an automatic machine which can work like a human being. It can replace man in various branches of scientific and industrial tasks because it does not suffer from human limitations. It may or may not resemble a human being but definitely can work like a human being. The robots which resemble humans are called androids.

          The word ‘robot’ was first used in the play ‘Rossum’s Universal Robots’ by the Czechoslovak dramatist, Karel Capek, who had derived it from a Czech, word ‘Robota’ which means a forced or bonded labourer.

          The industrial revolution and automations stimulated the invention of robotic devices to perform certain human tasks. A human worker, however superb a craftsman he may be has certain limitations. He cannot work continuously in a hostile environment. He cannot work for long periods because he gets tired. He may be in short supply and may be expensive to hire. Modern industrial robotic devices aim to substitute a machine for man in hostile environments, cut costs by replacing expensive hand labour with cheap dependable machines, and provide versatile, all purpose robots or mechanical devices at predictable costs. Robot is such a machine which does not get tired, does not go on strike and does not demand increase in salary. 

          Robots can perform a variety of jobs such as welding and painting a car, house cleaning, cutting the grass of a lawn, working in nuclear plants or travelling to space. They can also play chess, work as a watchman, cut the wool of a sheep and pluck fruits from trees.

          Robots of higher level are capable of adapting to changes in environment. They are also capable of making decisions with the help of computers. A more complex robotive device in modern transportation is the automatic aircraft pilot which can control routine flights. An android robot named Shaky Robot was developed at Stanford Research Institute in California to do a variety of research jobs.

          Japan has the largest number of robots in the world. The United States of America, Britain, Germany, Sweden, Italy, Poland, France, India, etc are also using robotic devices for different purposes. All robotic devices are controlled by computers.

 

Can air be converted into a liquid?

Scientists have developed techniques through which gases like nitrogen, oxygen, hydrogen, and helium can be converted into liquids. These techniques involve cooling of the gas to a certain temperature called the critical temperature and then it is compressed to a very high pressure. Due to this cooling and compression the molecules of the gas come closer and the gas gets converted into a liquid. Air is a mixture of nitrogen, oxygen and other gases and can be liquefied by cooling it to about -200°C at normal atmospheric pressure. Under high pressure it can be liquefied at about -141°C.

The technique used for the liquefaction of air is shown above. Through this technique the air from the atmosphere is compressed to a high pressure. This air is then allowed to expand rapidly. As a result, the air gets cooled to a very low temperature. Its heat is lost due to the sudden expansion. This cool air is compressed further by which it gets converted into liquid.

Liquid air is very cool. It is a mixture of liquid oxygen which boils at -183 °C, liquid nitrogen which boils at -196°C and liquid argon which boils at -186 °C. It is bluish in colour and is kept in special vacuum flasks. It is mainly used in research laboratories to produce low temperatures.

Liquid hydrogen boils at -253°C. It is cooler than liquid air. Liquid helium is still cooler. It boils at -269°C. All the liquid gases should be handled with care. If they fall on your skin they may damage the body cells. If a rubber tube is inserted in liquid air it becomes as hard as a wooden stick. 

How does soap clean things?

           Ordinary water does not remove dirt from things because grease and water do not mix. So soap is one of the most common cleansing agents used all over the world. People use soaps and detergents to clean their skin, clothes, utensils and many other objects. How does soap remove dirt?

          Soap is basically a fatty acid salt which can be obtained by boiling fats or oils together with an alkali. When oil is allowed to react with caustic soda solution, the chemical reaction produces soap and glycerin. Both are separated. When soap is applied on a cloth, its molecules break into fatty acid ions and sodium ions. Fatty acid ions are repelled by water but are attracted towards greasy dirt particles. They surround each grease molecule and remove it from the surface of the cloth. These are carried away by the water and consequently the cloth gets cleaned. Other actions, such as agitating, squeezing or rubbing and rinsing help loosen dirt and grease so that water may carry them away.

          Today, chemical cleaners called detergents are more and more in use instead of ordinary soaps. Detergents clean better than soaps in hard water, (the ‘hardness’ of the water is caused by the presence of calcium and magnesium salts. Soap does not make much lather in hard water) but they do not, by themselves, make suds. Suds are not necessary for cleaning but substances that make suds are added to detergents.

          Many substances are added to a crude soap to make it suitable for use as toilet soap. Coconut oil is added to make it lather quickly. Dyes, perfumes, water softeners and germicides, which are tiny substances that kill germs, are also added. 

How does an electron microscope work?

               Optical microscopes cannot magnify more than about 2500 times because the light rays can not produce a sharp image. The electron microscope is such a powerful instrument which can magnify minute objects by as much as a million times. It is used to study micro-organisms such as viruses, tissues and bacteria. We know that light travels in the form of waves. Similarly, waves are also associated with the moving electrons. These are known as matter waves. Electron microscope was constructed by making use of matter waves associated with electrons. Wavelengths of light waves are longer than that of the waves associated with electrons. Due to this reason an electron microscope has a higher resolving power and greater magnifications as compared to an optical microscope.

               The electron microscope works like an optical microscope with a condenser and objective and eyepiece (projector) lenses. The lenses are powerful magnets or electrodes.

               In an electron microscope a beam of electrons is focussed onto the object. With the help of electromagnetic lenses an enlarged image of the object is produced on a fluorescent screen. This image is photographed on a photographic film or plate. With the help of this photograph the object structure is studied in detail. Most of the big research laboratories make use of electron microscopes.

 

 

How does a Photostat machine work?

            Photostat or xerography is a means of copying documents, letters or pages of books without using liquid inks. This could be called ‘dry writing’.

            A photostat machine makes use of static electricity. It relies upon the special properties of an element called selenium. When the light falls on selenium’s surface its electrical resistance drops sharply.

            To copy a page, the operator places it face down, upon a horizontal glass window. The button is pressed on the photocopier and a bright light comes on to light up the page. Its image is projected onto a highly polished selenium-coated cylindrical drum through a lens. The drum is charged with static electricity.

            The place where the light reflected from the white parts of the page falls on the selenium drum, the electrical resistance of the drum drops. Selenium’s charge leaks away to the ground. The light does not reach the drum from the black areas of the page. The drum on these areas retains the electrostatic charge. Now the drum is covered with a special powdered black ink. The ink adheres to the drum where there is still an electrostatic charge and so the image of the document gets formed in powdered ink on the selenium drum.

             Now a sheet of plain white paper is pressed close to the drum. The paper develops a charge opposite to that of the drum by induction. This charge attracts the ink powder from the drum. The ink jumps from the selenium drum to the paper, thus transferring the image to the paper. The paper is heated before it leaves the machine. This melts the ink which sticks permanently to the paper, giving a reproduction of the original document.

            In another type of electrostatic copiers, the image of the page is projected directly on to the paper, which charges its surface. The paper then passes through a bath of toner and the particles cling to the charged parts of the paper to produce the copy.

 

What is solar energy?

           Solar energy comes from the Sun to the Earth in the form of light and heat. It can be converted into electricity by solar cells. Today, scientists are engaged in developing new techniques for the benefit of mankind.

           Experiments have shown that when sunlight falls on certain metals like potassium and silicon, electrons are emitted from their surfaces. These electrons are known as photoelectrons and this phenomenon is called photoelectric effect. Photoelectrons so emitted can be used to produce electric current.

           Photoelectric effect has been used for the making of solar cells. A solar cell, in fact, is a device that directly converts solar energy into electric energy. These wafers of silicon element are used for making solar cells. Generally, a four centimetre long and two centimetre broad and 0.14 millimetre thick silicon wafer is used for one solar cell. When sunlight falls on this wafer it gets converted into electric energy. Each solar cell is capable of producing about a half volt of electricity.

           To produce useful quantities of electric current, it is necessary to join together a great number of solar cells. The cells are joined together in big panels and are placed in the sunlight. A panel of about 20,000 solar cells can produce 500 watts of electric power. The electricity produced thus can be used either immediately or can be used to charge electric storage batteries for later use. Materials like cadmium sulphide and gallium arsenide are also being used for making solar cells.

           Solar cells have several different uses. In sunny places, solar panels are used to provide boost power to telephone signals. In space where the supply of solar energy is plenty, solar cells are particularly useful. Spacecrafts, space-laboratories and satellites have a number of solar panels to provide power for their equipments.

          The biggest solar energy furnace of the world is in California, USA. It uses almost 2000 mirrors, which focus the sun rays on to a boiler unit on top of a tower. This produces steam which is used to drive electricity generating turbines. In India, The Bharat Heavy Electricals Ltd. (BHEL) and Central Electronics Ltd. (CEL) are making cells that have found many applications.

 

How do we take a photograph with a camera?

A camera is the instrument that will give us picture of a person or a scene called a photograph that can be kept for sweet memory. It has become one of the most important means of communication and expression in modern times. Basically, a camera is a dark box fitted with a lens on one side. Just behind the lens there is an aperture which controls the amount of light admitted. A shutter exposes the film to the light for a short interval. A photosensitive film is mounted on the opposite side of the lens. This film has a layer of silver bromide coated on it.

The object, whose photograph is to be taken, is focused on the film. This is done with the help of another lens called a view–finder. On opening the shutter the light from the object enters the box through the lens. An inverted image of the object is recorded on the photo film.

The exposed film is taken out of the camera and developed by a chemical process. For developing the film a solution of quinol and metal is used. During this process the portion on which more light has fallen becomes darker and the image of the object appears in reverse tones. The developed film is put in the hypo solution for fixing the image. That is how the negative of the object is obtained. In the negative white portions appear dark and black portions appear white.

Now with the help of an enlarger, a print or positive is made from the negative. The light coming through the negative is focused on the photosensitive bromide paper. This paper, after developing and fixing, takes the shape of a positive. That is how we get the photograph of an object.

There are a lot of developments taking place in the field of photography. Nowadays, the techniques of making coloured photographs are being used on a large scale. Instant cameras take photographs in a few seconds. These instant cameras are called Polaroid cameras. Some special cameras produce motion pictures like TV and video cameras, the pictures are made electrically. Holography has given birth to three dimensional photography in which we can see the length, breadth and thickness of the object.

What is a dry cell?

          We make use of dry cells in our torches, transistors and cameras. As soon as we press the switch of the torch the filament of the bulb gets heated up and it begins to glow. Similarly, when we switch on our transistors sound is produced. These devices get their energy through the electric current produced by the dry cells fitted in them. There are three main types of dry cells: carbon-zinc, alkaline and mercury.

          A carbon-zinc dry cell consists of a cylindrical vessel made of zinc. A carbon rod with a brass cap is placed at the centre of this vessel. Zinc acts as the negative electrode and carbon as the positive electrode. A paste of ammonium chloride, zinc chloride, manganese dioxide and carbon is filled in the vessel around the carbon rod. The paste is further surrounded by another paste of plaster of Paris, ammonium chloride and zinc chloride. Plaster of Paris makes the paste hard. The zinc vessel is closed with a layer of pitch. Finally, the vessel is wrapped with a thin cardboard and we have a carbon-zinc dry cell. This cell is a lechlanche type of primary cell in which the electrolyte ammonium chloride is dissociated into positive and negative ions. These are attracted towards the electrodes and produce voltage. When they are connected with a wire, current begins to flow. In this reaction hydrogen gas is also produced and it is converted into water by manganese dioxide. These cells produce electricity till the whole of the manganese dioxide is used up to convert hydrogen into water. Manganese dioxide, after the reaction with hydrogen, gets converted into manganese oxide. After this conversion, no electricity is produced by the cell.

          An alkaline dry cell battery is more powerful and lasts eight times more than a carbon-zinc cell. It also has a carbon electrode and a zinc casing electrode. The electrolyte is a strong alkali solution which has potassium hydroxide. Alkaline dry cells are used mainly for portable radios.

          In a mercury dry cell, the voltage remains constant till the end of the life of the battery. A mercuric oxide electrode is used. The other electrode is the zinc casing. The electrolyte is potassium hydroxide.

          Why these cells are called dry cells? It is simply because its electrolyte is not in a solution form but in a paste form. It would become useless the moment the electrolyte dries up. Dry cells are adversely affected by high temperatures. Hence they should be stored in a cool place, away from direct sunlight. It is better to take out the cells from the torchlight, camera or transistor if they are not being used because moisture leaks out from the cell and it swells up. 

How does an airconditioner work?

An airconditioner is an electrically operated device used to keep houses, offices, and laboratories cool during summer and warm during winter. It not only controls temperature but also regulates humidity.

Today, airconditioners of all types and sizes are available. The big airconditioner plants are capable of cooling or heating an entire building.

          In general, an airconditioner keeps the temperature between 20°C and 25.5°C and relative humidity around 35-70%. An airconditioner plant consists of a compressor and a cooling liquid like the Freon gas. The cooling liquid evaporates in the cooling coil. This vapour is then carried to the electrically-operated compressor. It then goes to the condenser where it is cooled by air or water as it passes through the radiator. Here the vapour changes to a liquid giving off heat in the process. The compressor thus serves to transfer heat from one place to another. A fan sends fresh air into the room which keeps the temperature of the room to the desired level. The airconditioner has certain substances which remove the moisture from the room. It also has filters to remove the dust particles from the air. This is how an airconditioner controls the temperature and humidity and keeps the air clean. Some airconditioners have attachments so when turned on we get hot air in the winters.

          Many new buildings, factories and homes are now being designed to include air-conditioning. Ships, aeroplanes, cars, offices, restaurants, theatres, shops and space vehicles make use of this steady flow of comfortable, purified air.