The effects created by moving charges give rise to what we generally call electricity. In order for charges to move, they must be acted upon by positive or negative charges.

Work must be done in order to seperate positive and negative charges. When they're seperated, the charges have electric potential energy and would move if free to do so.

Consider the situation shown above. We start out with some unorganized charges and then begin to separate them. Very little work is needed to pull the first negative charge to the lift and the first positive charge to the right. When the next negative charge is moved to the left, it is repelled by the negative charge already there, so more works is desired. In a like manner, it takes more work to move the second positive charge to the right. As we separate more and more charges, it takes more and more work.

Instead of speaking of electric potential energy, we usually speak of a potential difference or more commonly, voltage. The voltage is defined as the amount of work it would take to move a charge between two points, divided by the value of the charge. That is, voltage is the work per unit charge, or the electrical potential energy per charge.

The volt (V) is the unit of voltage and is equivalent to one joule per coulomb. Voltage is caused by a separation of charge, once the charges are separated, a current can be set up, and we get electricity.

When we have a current, it meets with some opposition by reason of collision within the conducting material. The opposition to the flow of charge is called resistance. The unit of resistance is the ohm (, Greek letter omega). There is a simple relationship between voltage, current, and resistance that was formulated by Georg Ohm (1787 - 1854 ), a German physicist, that applies to many materials.

Bookmark This Page