A big part of understanding xerography has to do with what's called electrical charge.

There are two types of electrical charges, positive and negative. The important thing to know is that two objects that have opposite electrical charges on them (one is positive and the other is negative) will want to attract one another. This is what happens when you rub a balloon against your shirt and then stick it on the wall.

In a copier machine there is a special type of film called a photoreceptor that acts like the wall with the balloon stuck to it.

This photoreceptor is very special because if it gets charged up you can "erase" the charge by shining light on it (that's what photoreceptor means - receiver of light).

You will soon see why this is very important. When you press the button on a copier machine, several steps using electrical charges follow. First, electricity passes through a thin wire which is held just above the photoreceptor. This electricity causes the air to form lots of positive charges that are sprayed onto the photoreceptor.

Next, a beam of light, such as that from a laser is used to "write" on the photoreceptor. Remember, wherever light hits the photoreceptor the charge is erased. Where this beam writes depends on what the original sheet of paper you placed into the copier looks like, for example what numbers or words are on it.

The light beam will write on the photoreceptor where the numbers and letters are not supposed to be, causing the charge to be erased there. Where the bean doesn't hit the photoreceptor, the charges remain giving a pattern that looks just like letters and numbers on your papers.

A black or colored powder called toner is shaken over the photoreceptor. The toner particles are like balloons that stick to the wall. The toner has a negative charge and therefore sticks to positive charges that were left on the photoreceptor.

Next, a piece of paper is pressed against the photoreceptor to make the toner transfer to the paper. Finally, the paper is heated to make the toner melt into the paper so it won't rub off.

Out comes your copy. So, next time you stick a balloon to the wall, remember that electrical charges can be used to do some really useful things!