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Sunday, 21 November 2010

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Science:

Electricity and magnetism

Today we light up our homes and use appliances such as televisions, irons and various types of machinery both at home and in factories because of electricity. This electrical power which has become indispensable to us is generated either by water, gas, coal or fuel. Electricity can be converted into light and heat.

Magnetism, a force that acts between magnets is all around us and is used to produce large amounts of electricity. Magnets can be found in telephones, televisions and radios.

Thousands of years ago, the Greeks discovered that a stone called amber attracted light weight objects. The Greek word for amber is 'electron.'

Do you know that we humans have natural electricity in our bodies? It helps carry signals and messages along nerves. Our bodies can conduct electricity, especially when they are wet.

It is dangerous to touch plugs, sockets or light switches with wet hands, bcause of this.When we want to direct electricity to some particular point we use conductors but if we want to prevent it from reaching any place, we use insulators.

Water and metal are good conductors of electricity.However, not all materials are good conductors of electricity. Plastic and rubber does not allow electricity to travel through it. That's why insulators are made from this material.

Most materials are made of atoms that are electrically neutral. However, if these atoms gain tiny particles called electrons they become negatively charged. On the other hand if they lose the electrons, they become positively charged. Just as much as two positively charged atoms or negatively charged atoms repel each other atoms which are opposite attract each other.

So, when a material that does not pass electricity is rubbed against one that allows electricity through, a charge of static electricity can be produced. Rubbing or friction causes static.

We experience static daily. Nature's most spectacular display of static electricity is a flash of lightning. During a thunderstorm, raindrops and hailstorms hurl up and down inside a thunder cloud producing charges of static electricity. Positive charges move to the top of the cloud while negative charges remain at the bottom.

The Earth under the clouds are positively charged. So, what do you think happens? The negative charges in the clouds are attracted downwards to the positive charges.

This is why lightning can occasionally strike earth and we need to take precautions. Would you believe that the hottest part of a flash of lightning can reach a temperature six times hotter than the surface of the Sun?


James Watt


Hans Oersted


Michael Faraday


Thomas Alva Edison


George Simon Ohm

Many people contributed to make it possible for electricity to be used in our day-to-day activities.

In the nineteenth century, a Danish Scientist named Hans Oersted first proved the relationship between electricity and magnetism when he noticed that a magnet held near a compass caused it to turn. When an experiment was done replacing the magnet with a current of electricity, he observed the same effect. This was the start of electromagnetism.

The English physicist, Michael Faraday discovered that electrical energy could be turned into mechanical energy (movement) by using magnetism. Using a cylindrical coil of wire called a solenoid, he created a simple electric motor.

He also discovered that mechanical energy can be converted into electrical energy-which was the reverse of the principle of the electric motor. And his work led to the development of the dynamo or generator we use today.

Due to the scientific experiments with electricity and magnetism carried out by men like Faraday it is now possible to make large amounts of electricity which can be carried along wires to our homes or factories like water in a pipe, from a power plant.

Two men were responsible for the incandescent (white hot) electric light bulb. They are Thomas Alva Edison, an American and Joseph Swan, an Englishmen. Edison's light bulb was first produced on October 21, 1879. James Watt, the inventor of the steam engine gave his name to the measurement of electrical power - the watt while German scientist, George Simon Ohm gave his name to the measurement of electrical resistance.

Today, electrical resistance which is what makes the filament (long, thin piece of wire in a bulb) glow and the element of an electrical heater glow, is measured in ohms.

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