Category Physics

What is the Zodiac?

            In ancient times, when people looked up at the sky in the night, they observed many bright stars arranged in a certain pattern or group. Each group is called a constellation. It means a group of stars. Studies of movements of these constellations led to the discovery that they move in space in fixed directions. The number of constellations visible during the year at different times was found to be 12. The Sun and the Moon were always seen rising and setting in the same directions in which these twelve constellations were located. These 12 constellations were called the signs of the zodiac.

            The hypothetical part of the sky through which the Sun, the Moon and other planets seem to be passing is called the zodiac. Each of the 12 constellations situated at an angle of 30°, is named as a different sign of the zodiac. In this way the 12 signs of the zodiac have come into existence. Each sign is connected with one constellation and the shape of each constellation resembles certain earthly body or substance. The names of these signs and the position of the Sun are as follows:

  1. Aries: The Ram – 21 March to 19 April
  2. Taurus: The Bull – 20 April to 20 May
  3. Gemini: The Twins – 21 May to 21 June
  4. Cancer: The Crab – 22 June to 22 July
  5. Leo: The Lion – 23 July to 22 August
  6. Virgo: The Virgin – 23 August to 22 September
  7. Libra: The Balance – 23 September to 23 October
  8. Scorpio: The Scorpion – 24 October to 21 November
  9. Sagittarius: The Archer – 22 November to 21 December
  10. Capricorn: The Goat – 22 December to 19 January
  11. Aquarius: The Water Bearer – 20 January to 18 February
  12. Pisces: The Fish – 19 February to 20 March

     

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What is lunar eclipse?

            When we stand in the sunlight, the rays of the Sun fall on us and we can see our shadows. Exactly like this, shadows of the Earth and the Moon are also formed in the space due to the Sun rays falling on them. Since the Earth and the Moon are spherical in shape, their shadows are conical in shape. These shadows are very long. The larger the distance of a body from the Sun, the longer will be its shadow. Lunar eclipse is darkness on the Moon due to the Earth’s shadow over a portion of it.

          While making their revolutions, the Sun, the Earth, and the Moon come in a straight line and the Earth sometimes comes in between the Sun and the Moon, thus the shadow of the Earth falls on the Moon. In other words, the Sunlight does not fall on the Moon when the Earth comes in between the two. The portion over which the shadow falls becomes dark. This is called lunar eclipse. Such a situation occurs only on Purnima (full Moon) days. Therefore, the lunar eclipse takes place only on that day. If the Earth’s shadow covers the entire Moon, it is total lunar eclipse. If the shadow covers only a part of the Moon, it is partial eclipse. Generally, there are three lunar eclipses in a year, out of which one is a total lunar eclipse.

             Now the question arises: when the full Moon comes every month, why does lunar eclipse not take place every month? The reason is that the plane of the Moon’s orbit makes an angle of 5° with the plane of the Earth’s orbit. Consequently, the Moon revolves either above or below the Earth’s shadow. So, it is only twice or thrice a year that all the three – the Sun, the Moon, and the Earth – come in one straight line. Hence the lunar eclipse does not take place every month. Astronomers, using mathematical calculations, easily predict the time and duration of the lunar eclipse.  

What is a Compact Disc?

            Compact disc is a new kind of disc which is recorded and played by laser beam. Compact disc has silvery, mirror-like surfaces which reflect light in a rainbow spectrum. The music disc is about 12 cm dia. while video disc is about the size of an LP and hold both pictures and sound.

            In the recording process, sound signals are converted into number so that each part of the signal has a precise code. These numbers are recorded as the binary digits 0 and 1. Physically, sound is recorded on a CD as a series of minute pits and flats which relate to the two digits.

           The laser disc has a very reflective metallic surface, covered by a protective coating of clear plastic. A semiconductor or small He-Ne laser is used for scanning. The player spins the disc and scans with laser beam which moves straight across the disc from the centre to the edge. The shiny surface reflects the beam back into the player, where it is picked up by electronic device. This produces an electrical signal which the player decodes back into video pictures and sounds. The laser beam reads about 20,000 digits every second which are converted into sound signals.

           The biggest advantage of compact discs is that they never wear out because there is no physical contact between the disc and the player – only a beam of light. 

What is the principle of an autopilot?

Most large planes have an autopilot. This is a device operated by a computer. It will fly the plate without the pilot’s touching the controls. These autopilots can even control take offs and landings.

 

 

 

 

 

 

 

The principle of an automatic pilot is similar to the automatic steering of ships, but here three gyroscopic sensors and their associated equipment are used to control the three variables in aircraft position.

These three variables are yaw, pitch and roll. The complex autopilot system uses an airborne computer which activates servomotors for introducing necessary corrections. A radio or radar link to the computer allows control from the ground for automatic takeoffs and landings.

 

What is bar code?

A bar code is computerized information encoded in a pattern of black and white stripes. The black and white lines represent IS and OS and can be read by light. They carry encoded information – from the membership number of a sports club to the price and stock number of a packet of washing powder in a supermarket. In fact bar codes are used to store data of all kinds.

The code is scanned by a beam of light. When a beam of light is passed over the bar code only the white stripes reflect back the light. This is picked up by a photo – detector which produces a pulse of electricity when it receives light. So the black and white bar code is translated into on/off pulses of electricity. These pulses are fed into a computer for decoding. Nowadays laser beams are being used for reading the bar codes.

What is LPG?

         The term LPG stands for liquefied petroleum gas. LPG is commonly used for domestic cooking purposes. It is supplied in gas cylinders that need to be replaced when their fuel contents are consumed. The supply in gas cylinders contains a mixture of liquefied butane and iso-butane under pressure. The mixture remains a liquid under pressure but the highly volatile liquid fuel in the cylinder evaporates when pressure is released. The gaseous mixture starts going into the burner of attached stove or oven. Here it is ignited and the blue flame is used for different purposes.

         LPG is used as a cooking fuel. This is also used in water heaters, space heaters and furnaces. This gas is also used to heat incubators and brooders, to sterilize milking utensils and other equipments, dry fruits and vegetables and prevent frost damage.

         Moreover, LPG is highly combustible and forms an explosive mixture with air, therefore, any leakage followed by its mixing with air can cause a severe explosion just by the ignition of one match stick. In order to make gas leakage easily detectable some strong smelling substance is added to LPG. Before igniting the match stick we should be sure that there is no such smell near the gas cylinder or in the kitchen.