Where did the chalk come from?

Have you ever wondered where the chalk comes from? Well, it originates from the shells of single-celled marine animals known as foraminifera and from the calcareous remains of single-celled algae called coccolithophores!

When foraminifera, coccolithophores and other organisms die, their remains sink to the bottom and accumulate as a fine-grained marine sediment known as ooze. These deposits, built up over many, many years, eventually consolidate into chalk rocks and give rise to chalk cliffs above sea level due to the movement of Earth. Such cliffs are found in many parts of the world.

So, chalk is nothing but the white or light grey, porous limestone composed mainly of calcium carbonate quarried from chalk cliffs. Chalk is used for making lime and Portland cement. Finely ground and purified chalk is used as a filler in a wide variety of materials, including ceramics, putty, cosmetics, crayons, plastics, rubber, paper, and paints.

Much of the early blackboard writing was done with pieces of natural chalk. But today blackboard chalk is made from gypsum or calcium sulphate manufactured from other sources of calcium carbonate. Gypsum chalk is the softest and writes smoothest; however, it produces more dust than natural chalk.

Picture Credit : Google

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.