Salt properties Water is a polar molecule having both positive and negative ends. A salt crystal is also held together by the force of attraction between positively charged sodium ions and negatively charged chloride ions. When a salt  crystal is put in the water, the positively charged hydrogen ends (H+) of the water molecules get attracted to and surround the negatively charged chloride ions (Cl–). Thus the negatively charged oxygen ends...

A Heater Mechanism  The air above the heater becomes warm. Warm air expands and rises up tin to the air. Cool air comes down and replaces it this air too gets heated and rises up. This process keeps on repeating till the whole room gets heated up.

How do we hear sounds? The human ear has three main parts—the outer ear, middle ear and inner ear. When a sound or noise is produced, the air particles next to its source, start vibrating and these vibrations travel in waves to the external ear which picks them up and funnels them towards the eardrum. The eardrum vibrates when the vibrations I hit it. Three tiny bones inside the middle ear...

Television and its Programme System Each T.V. station uses a different signal with a different frequency than other TV stations. Our T.V. antenna catches all these signals and pass them into the set as electrical signals. When we tune in to a particular channel, the tuning coil starts oscillating at a particular frequency showing us a programme. When the channel is changed, the frequency of the tuning coil is also changed...

Minerals Extraction  Minerals occur in the earth’s crust through-out the world. Depending upon the nature and location of the minerals, various methods are used for their extraction. Excavation is one such method in which mechanical excavators scoop out the surface rock and sediments so that the useful minerals like gravel, coal. sand etc., which occur near the surface of the earth, can be extracted. Drilling is done to reach deep deposits...

Our Counting of System The cave man used, his fingers, or toes for counting. The word ‘digit’ is derived from the Latin word digits meaning finger. I Since we have 10 fingers, the use of fingers led to a system of counting built on base 10. With the time, new counting tools like stone, tally marks, knots on ropes, notches on sticks came up. Then came the counting machine called ‘Abacus’...

The Sun Sun is a huge ball of hot gases that nobody can go near it, leave alone landing on it. Still then the scientists have found out what the sun is made of by using special instruments. Some of them are spectroscope, radio telescope, spectrohelioigrahp, spectrograph, chronograph and space probe. A spectroscope studies the glowing gases of the sun and tells us about the chemicals which produce the colours in...

Telescope Powerful telescopes are used to observe the space. Presence of stars, not visible even through powerful optical telescopes, is determined by even more sophisticated telescopes like radio telescopes etc. These telescopes can detect radio waves, U.V. rays and X-ray signals which are emitted by distant stars and other celestial bodies. These days probes or unmanned satellites, remote sensing satellites etc. can record the photographic images of these celestial bodies.