Static Electricity.

Fig.1 Van Degraaff generator.

All matter is normally electrically neutral; because the molecules have an equal number of electrons and protons. As they absorb a specific form of energy the electron moves into a higher orbit. At times the electrons can even leave the atom. This will leave a positively charged unit known as a positive ion(cation).

Fig. Forming a cation.

We generally know electricity as the flow of electrons. Electric current suppose to flow from positive to negative although the electrons travel the other way. Electrical energy can also be stored up. We call this Static Electricity. Fig.1 shows a device that can store electrical charges at a very high pressure.

Fig.2 Charges in a Van degraaff generator.

As the rubber belt rotates it comes into close contact with the polythene roller. As the belt separates it peels off a few electrons giving the roller a positive charge. The electrons are taken up by the belt. There is a piece of metal called a comb with pointed ends that pick up electrons and transfer them to the outer surface of the metal globe. As the charges cannot leak out from the globe it is possible to get a very high potential difference between the globe and the environment.In some machines this can go upto millions of volts. Yet it would be harmless and possible to get a spark to your body. It cannot do any harm as the current would be very low.

In this set up the globe gets a negative charge. In some models the globe can be made to get a positive charge.

What causes the electron transfer?

It was earlier thought that, the rubbing action (friction) that produced electricity. That is not what really happens. In this case there is no rubbing at all. Friction only makes the pulley turn.

When certain substances come into close contact with another substance, electrons of neighbouring molecules form certain links. This is called adhesion. When they separate some materials have the ability to take a few extra electrons. Then that substance will carry a negative charge while the other gets a positive charge.

So you can guess, what would happen if you comb your hair with a plastic comb. The comb will be able to pick up pieces of paper?

There is a series arranged according to the ability to pass on electrons on close contact called the Triboelectric Series. This is not a foolproof arrangement such as the electrochemical series but varies according to conditions, such as humidity and temperature.

Measuring electric charges.

The SI  unit of electric charge(Q) is the coulomb (C).

Coulomb is the quantity of electricity conveyed in one second when a current of 1 Ampere flows through.

Formula:-         Q= it.    

                       That is Coulombs = amperes x Seconds.

Fig.3. Force of lines resulting from charges.

Electrically charged matter produces, electromagnetic fields.

Electric field is defined as the electric force per unit charge.

The direction of the field is taken to be the direction of the force it would exert on a positive test charge.

The electric field extends outward from a positive charge and inward in the case of a negative charge.