Category Science

When was the first artificial satellite launched?

           A satellite is a body that orbits around another but the term is usually applied to small bodies which orbit around the planets. Most of the planets have satellites revolving around them. For example, moon is the only satellite of earth. But apart from the natural satellites of the planets, several man-made or artificial satellites have been launched which now orbit the earth and some of the other planets in the solar system. But when did man send the first artificial satellite into the space? 

          The first artificial satellite was launched into the space by the former USSR on 4 October 1957 which was called Sputnik I. Sputnik is the Russian word for a travelling companion. It was spherical in shape with a diameter of 58 cms and weighed 83 kilograms. It orbited the earth every 96 minutes. A month later the launching of Sputnik 2, which weighed 500 kg, created another landmark in the space history as it carried the first ever space traveller, a dog named Laika. This established the fact that a warm-blooded animal could live in space thus paving the way for man’s venture into the space which finally succeeded in 1961 when Yuri Gagarin of USSR orbited the earth in his spacecraft Vostok I.

          The first American satellite was Explorer I which was launched on 31st January 1958 and weighed only 14 kilograms. The first American astronaut to be in space was John Glenn in 1962. The first woman space traveller was Valentina Tereshkova of USSR.

          But what functions do these artificial satellites perform in the space? They are used for radio and TV communications, weather forecasting, geological surveys, telecommunications, defence and spying purposes, scientific studies like space and astronomical observations, crop patterns and oceanography. Depending on their function they are called communication satellites, weather satellites, scientific satellites, earth resources satellites etc. Some satellites perform a number of functions and are called multipurpose satellites. 

What is the Nitrogen Cycle?

          Our atmosphere contains about 78% of nitrogen. A certain amount of this nitrogen is constantly being removed, and an approximately equal amount is being returned. This continuous circulation of nitrogen among the soil, water, air and living organisms is known as the Nitrogen cycle. Let us see how the percentage of nitrogen in the air remains constant.

          All living things need nitrogen. It is part of proteins and nucleic acids, both of which are vital for life. How nitrogen is removed from atmosphere and again returned to the atmosphere is given below.

          A part of the atmospheric nitrogen is removed from the air by lightning. The sudden discharge of electricity causes some of the nitrogen and oxygen components in the air to combine, forming the oxides of nitrogen. When these nitrogen oxides are dissolved in water, they combine with other elements to form nitrogenous compounds.

          Some nitrogen is removed, from the air by certain bacteria and algae in a process called nitrogen fixation. Symbiotic bacteria present in the nodules of roots of some plants, such as peas, beans, gram etc. take up atmospheric nitrogen directly, and pass it on to the plants. Plants take up nitrogen compounds and convert them into proteins. These proteins are assimilated by animals. Some other plants, like rice, have symbiotic blue-green algae which fix atmospheric nitrogen.

          As a result of death, decay and excretion by plants and animals, the organic matter is converted into ammonium salts in the soil. Special nitrifying bacteria convert ammonia into nitrogenous compounds that are used up by plants. Animals get their nitrogenous compounds by eating plants, or other animals that eat plants.

          Thus an approximately equal amount of nitrogen is also being constantly returned to the atmosphere. Denitrifying bacteria change some of the nitrogenous compounds in the soil, back into gaseous form of nitrogen. These gases then return to the air.

          Thus nitrogen from the atmosphere passes into the soil, plants and animals and finally returns to the air. It may take thousands or millions of years, but every molecule of nitrogen eventually returns to the air.

 

How do astronauts walk in space?

          It appears strange but true that astronauts can walk in the space. This is so because in ordinary walking we rest our feet on the surface of the earth and the force of earth’s gravity pulls us towards it. But when there is nothing in the empty space – neither any surface to walk on nor any gravitational force to pull the feet down onto the ground – how does an astronaut walk in the space?

           Space walking by astronauts is quite different from the normal walking. To walk in the space the astronauts take the help of hand rockets which provide them the force to move. The hand rockets follow the principle of rocket propulsion. In rockets, the ejection of gas with a great force from the backside pushes the rocket forward with an equal thrust. This working principle is based on Newton’s third law of motion which states, ‘To every action there is always an equal and opposite reaction’. Similarly in hand rockets when the engine is powered the exhaust thrust pushes the rocket in the opposite direction and the astronaut walks along with this force as he carries the hand rocket with him. In fact, it is not ‘walking’ in the strict sense as there is no surface in the space to rest the feet but rather ‘floating’ – to express more accurately.

          But why do the astronauts walk in the space? Apart from experimental reasons, sometimes they are required to shift from one spacecraft to another or need to carry out a repairing work on the outer surface of the craft. During such operations they use the specially designed hand rockets and the direction of the exhaust outlet is pointed opposite to the desired direction of walking.

          The first spacewalk was made in March 1965 by a Soviet astronaut, A. Leonov, who stayed outside the aircraft for 24 minutes. Another important walk was made in 1973 when the American satellite Skylab was to be repaired for damage in the heat shield that made the craft dangerously hot. 

What is magnetism?

          Magnetism owes its name to the fact that the early Greeks found the natural magnetic material called Lodestone, in an area called Magnesia, a province of Asia Minor in 800 B.C. This stone was of black colour and an ore of iron called magnetite. This stone has several interesting properties.

          Firstly, it has a strong attraction for iron. On experimenting, it was found that if a piece of lodestone was dipped in iron fillings and then lifted out, the fillings mainly get attached to certain parts, the other parts remaining bare. These regions of greatest attraction were called the poles and the place where there was little attraction was called a neutral region.

          It was also discovered that if a piece of lodestone was suspended by a thread or floated on a piece of wood, it came to rest in a definite direction — pointing towards north and south. The part pointing towards the north was called the North Pole, and the one pointing towards the south was called the South Pole. This property was used by the Chinese in the 13th century to make use of magnets as compasses for finding the direction in sea voyages.

          Experiments in this field further revealed that if two lodestones were brought together, the north and south poles attracted each other while the north-north and south-south poles repelled each other. This established the fact that dissimilar poles attract each other and similar poles repelled each other.

          If a bar of iron or steel is rubbed from one end to the other end with a piece of lodestone, it also acquires magnetic properties and becomes a magnet. Such a magnet is known as an artificial magnet.

          Gradually scientists working in this field also discovered that a magnet could be made by winding an insulated wire around a piece of iron and passing an electric current through it. This is called an electromagnet. Such magnets are used in electric motors.

          The next important discovery in the field of magnetism came in 1600. The English scientist, Sir William Gilbert, suggested that the earth was a giant magnet. Thus he explained why a freely suspended magnet points to the north and south of the Earth. 

Continue reading “What is magnetism?”

What is a Kaleidoscope?

A kaleidoscope is an optical instrument used to produce symmetrical geometric patterns on carpets, sarees, wallpapers etc. It is also an entertaining toy for the children.

Kaleidoscope was invented by a Scottish physicist, Sir David Brewster in 1816. It illustrates the image forming properties of combined inclined mirrors by successive reflections. If one object is placed between two plane mirrors, at right angles to each other, three images are produced by successive reflections. Similarly, if the mirrors are inclined at 60°, five symmetrical images are formed.

A kaleidoscope consists of three strips of mirrors inclined at an angle of 60° to one another. They are enclosed in a cylindrical tube. One end of this tube is closed by means of a piece of ground glass, while the other is closed by a piece of cardboard with a hole at its centre. Several multi-coloured glass pieces and beads are loosely enclosed between the three inclined mirrors with the help of a disc made of plane glass. Now when viewed through the hole of the cardboard, along the axis of the tube, a symmetrical pattern of images of the coloured glass pieces are seen.

When a person turns the kaleidoscope, the coloured glass pieces and beads change positions, thereby new patterns are produced. And so in this manner, an infinite number of combinations and patterns can be formed. The tubes used in most of the kaleidoscope are usually 25cm in length and 5 – 8cm in diameter. It is a very useful instrument for the designers. 

What are ultraviolet rays?

          Ultraviolet rays are electromagnetic waves that cannot be seen by the human eye. When sunlight is allowed to pass through a prism, it splits into seven colours. These colours are violet, indigo, blue, green, yellow, orange and red. Wavelength-wise distribution of the seven colours is known as spectrum. The ultra-violet rays form an invisible band, just outside the violet end of the visible spectrum. The band just beyond the red end is called infrared.

          Light travels in the form of waves. These waves are produced by electrical oscillations. The frequency or wavelength of each colour in the spectrum is different. Frequency is measured by the unit ‘hertz’. If a body vibrates once in a second, its frequency is said to be one hertz.

          In the seven colours of the sun’s spectrum, violet has the maximum frequency and red has the minimum frequency. In other words, wavelength of the violet colour is minimum, while that of red is maximum.

          The observed wavelengths in the visible spectrum range from about 7.5 x cm to 4 x  cm. Waves having wavelengths more than that of red light is called infrared waves. Infrared radiations comprise wavelengths ranging from 1 mm to about 7.5 x  cm. Waves having wavelengths more than infrared radiations are called microwaves. The range of microwaves lies between 1 mm to 30 cm. Waves with wavelengths more than those of microwaves are called radio waves. On the other hand, radiations having wavelengths less than that of violet colour are called ultraviolet rays. Ultraviolet rays lie in the wavelength range of 4 x  to   cm. Beyond ultraviolet rays come X-Rays which roughly lie in the wavelength range of   to   cm. Beyond X-Rays come gamma rays. As we go from ultraviolet rays to gamma rays the wavelength decreases or the frequency increases. As the frequency increases, the amount of energy associated with the waves also increases. Thus X-Rays and gamma rays are very high energy radiations.

          Energy associated with ultraviolet rays is also quite high. Overexposure to ultraviolet rays can cause skin burns, and may even lead to skin cancer. The sun produces a large amount of ultraviolet light most of which are absorbed by a gas called Ozone, in the upper atmosphere of the earth and as a result very small amount reaches the earth. If the entire amount of ultraviolet light were to reach us, life wouldn’t have been possible on earth.

         Ultraviolet rays are useful also but only in small amounts. They kill certain bacteria and help to change certain chemicals in the skin into Vitamin D. These rays are very harmful for the eyes as they cause eye-cataract. While working with ultraviolet light, one must wear coloured glasses. When these rays fall on certain substances, they produce fluorescence.