Category Science

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.

 

Why are fireworks colourful?

                Fireworks (crackers etc.) are used on various occasions of national, religious and social festivals in almost all the countries of the world. It is estimated that every year a sum of Rs. 5000 crores is spent all over the world on fireworks of about 300 varieties. When they are ignited, they explode and present a riot of colours. Do you know why they are so colourful?

              Fireworks are prepared by a mixture of potassium nitrate, sulphur, coal and salts of certain metals. The colour is provided by salts of metals like strontium, barium, magnesium and sodium. They are mixed with potassium chlorate. Barium salts give out green colour, while strontium sulphate produces light sky blue colour. Strontium carbonate produces yellow colour whereas strontium nitrate produces red, salts of sodium impart yellow colour, those of copper impart blue colour. Aluminium powder in the fireworks produces the silvery rain. When fireworks explode these salts burn in fireworks, various colours come out and present a spectacular sight.

                    China was the first country to manufacture fireworks.

                    Hundreds of years later, Europe, Arabia and Greece also manufactured them. At present, a small town in India named Shivkashi manufactures the largest amount of fireworks in the country.

                    Some time ago, in a celebration in Japan, colourful fireworks were lighted that went up to a height of 915 metres and were scattered in a radius of 305 metres. 

What is echo?

            When we speak loudly in a big empty hall or in a temple, we hear our own sound repeatedly. This is called echo. An echo can also be heard by shouting near a deep ditch or a well. The thunder of clouds is another example of echo.

             We know that sound travels from one place to another in the form of waves. The velocity of sound in the air is 340 metres per second. When we speak, the sound waves emanating from our mouth spread out in all the directions. When these waves meet a wall or some other obstacle in their way, they are reflected back. These reflected waves are heard by us as an echo. Hence echo is produced when sound waves are reflected by some obstacle. But all objects do not reflect sound. There are some objects like wood, jute, cardboard etc. which absorb sound.

              To hear an echo, it is essential that the obstacle reflecting the sound waves must be situated at least at a distance of more than 17 metres from us. This is because the effect of sound persists on our ears for one-tenth of a second. If one sound signal has reached the ears and within one tenth of a second another sound signal reaches our ears, it will not be distinguished because during this period the effect of the earlier sound is persisting in the ear. Sound travels about 34 metres in one-tenth of a second. As such, if the object reflecting the sound waves is situated 17 metres away from the speaker, the time taken for the sound to travel this distance from the speaker’s mouth to the object and back to him would be one-tenth of a second and the reflected sound can be distinguished by our ear as an echo.

              In Modern buildings architects use methods and materials which reduce echoes and favour good sound transmission. Auditoriums are built with rounded corners and few large flat surfaces. This prevents sound-waves from being reflected to any one position. They are scattered in many directions and the only sounds heard are those sent out from the source. Some fibre-boards having many holes are used for making rooms sound-proof. By the use of these materials the sound-waves are either absorbed or scattered so that production of echo is reduced. Radars and sonars work on the principle of echo. 

 

Why does the rising and setting Sun appear red?

When the sun rises in the east, it appears like a red ball. As the day advances, its colour appears white, but again at the time of sunset in the evening, it appears red. Do you know why it is so?

We know that our earth is surrounded by the blanket of air called atmosphere. Sunlight passes through the atmosphere before it reaches us. We also know that sun light is composed of seven colours – Violet, Indigo, Blue, Green, Yellow, Orange and Red. In the mornings and evenings, when the sun is near the horizon, the rays have to travel about fifty time’s longer path in the atmosphere to reach us than it does in the noon. The dust, smoke and water vapour present in the atmosphere scatter away these colours differently. Violet, indigo and blue are scattered most and red and orange are scattered least. That is why most of these two colours reach our eyes. As a result, the rising and setting sun appears red. 

 

How are the Pearls formed?

  Pure pearls are very precious. You will be surprised to know that only a small sea-creature, oyster makes them. An oyster can crawl on the ground also. The biggest tragedy with this little creature is that fish of the sea or the bigger members of its own family eat it away. When the oyster comes to the sea-shore to save its life, man eats it. In order to protect itself, it forms a hard shell around its body with a unique substance called ‘nacre’ or mother of Pearl. Pearls are made within this hard cover.

             The discovery of pearls is an interesting story. Some four thousand years ago, a Chinese was suffering from hunger. To satiate his hunger he opened some oysters to eat. Inside one oyster he found one small round shining ball. The shinning ball-like thing was later on called pearl.

              Whenever, by chance, a sand particle goes inside the shell of an oyster and rubs against the animal’s tender body in order to soothe this irritation, it starts depositing layers upon layers of the shell material on this particle. These layers are made up of calcium carbonate. After sometime the formation of the pearl inside the shell is completed. The pearl so formed is round, white and shining. This is called pure pearl. However, the pearls are not essentially white only. Their colours may be black, white, rose, pale blue, yellow, and green, mauve also.

                Man has now developed some techniques of making artificial pearls. Under these techniques sand particles are introduced inside the shell. After two or three years, when the shell is taken out of water, a pearl is found inside it. These pearls are called cultured pearls. Japan has perfected the technique of making beautiful cultured pearls. Since pure natural pearls are very costly, generally we purchase pearls developed by these artificial techniques. On the 7th May, 1934, a pearl was found in Philippines measuring 23 cm with a diameter of 13 cm. This pearl weighed about 6.37 kg. This pearl was called Pearl of Laozi.