Sample Material of Our Online Coaching Programme

Subject: General Science

Topic: Gist of What, Why and How

Radars Work

The word radar stands for radio detecting and ranging. It makes use of very short radio waves called microwaves. Radars work to find out how far away an Object is and in case of a moving object in what direction it is moving and at what speed.

Color TV Picture Produced

The picture on a television screen is nothing but a pattern of glowing dots, or pixels. The pixels are made up of fluorescent chemicals called phosphors that are coated on the back on the screen. These glow on being hit by a beam of a single phosphorus and are lit up by a single electron beam that rapidly sweeps across the screen. In a color television how-ever, each pixel contains three phosphorus each producing a different colour-green, red and yellow. Three electron beams produced by three electron guns are used to light up the different phosphorus.

Fire Extinguishers Work

Fire extinguishing agents work basically in two ways – either by cooling the burning materials or by blanketing them with an inert coating that cuts off the supply of oxygen. One of the most common ones uses water which has a high heat capacity.

Foam type fire extinguishers use foaming agents that have a smothering and cooling effect on the wire. A dry chemical extinguisher sprays a very fine power of sodium bicarbonate or potassium bicarbonate or monoammonium phosphorus. These solids coat the fuel and smother the fire. A safe and effective extinguisher for all confined fires uses carbon dioxide (co2) which acts as an inert blanket.

Lie Detectors Work

A lie detectors work on the principal that a person who tells a lie is nervous and under stress under these conditions his body undergoes some physiological changes.

These includes increases in the blood pressure, heart beat rate and perspiration on hands and soles. These changes are monitored and detected by a lie – detector.

Storage Batteries Work

Storage batteries are devices which act as a store house of electrical energy. The electrical energy is stored in the form of a chemical charge which is reversible. The most common storage battery is the lead acid- accumulator which uses lead as electrode and sulphuric acid as an electrolyte. Initially both the cell electrodes of the battery made of lead are coated with a layer of lead dioxide. When the battery is charged for the first time, chemical charges take place. During discharging when the battery is in use, chemical changes take place again but in the reverse way. Each cell in a lead – acid battery produces two volts and a typical car battery with six cells gives 12 volts. Nickel – iron and nickel – cadmium batteries are other kind of storage batteries which are nickel, and iron or cadmium as electrodes and potassium hydroxide as electrolyte.