A charge q in an electric field has electric potential energy. The work done on a charge in moving it from one point to another is equal to the change in electric potential energy:

Work = Change in Potential Energy

The potential energy of a charge depends not only upon the surrounding charges which are producing the electric field. It also depends upon the magnitude of the charge itself. For this reason, we define the electric potential at a certain point in space as the potential energy of the charge divided by the charge itself:

Potential = potential energy/charge.

Thus we have the equation that

W = (V2 − V1) q , where V1 = the potential at point 1 and V2 = the potential at point 2; W = work done in moving the charge from point 1 to point 2, and q = charge.
 
The unit of potential is the volt = 1 joule/coulomb. As we shall see, the charge of an electron is 1.6 × 10−19 Coulombs. An electron volt is the amount of energy gained by an electron when it fall through a potential difference of 1 volt.

  1. Draw a sketch showing the difference between high and low potential energy in the case of a) gravity b) an expansion spring c) a positive charge in the vicinity of a group of positive charges d) a negative charge in the vicinity of a group of positive charges e) a positive charge in the vicinity of a group of negative charges f) a negative charge in the vicinity of a group of negative charges.
  2. Explain the difference between potential and potential energy?
  3. A 5-C charge is transferred through a potential difference of 90 Volts. a) What work is done on the charge? b) What is the potential energy of the charge as a result of the transfer?
  4. A generator transfers 1.0 C of charge through a potential difference of 110 V a) What work does the generator do? b) What is the potential energy of 1.0 C of charge after the transfer?
  5. What work is done by the chemical energy of a dry cell to transfer 5.0 C of negative charge from its positive plate to its negative plate? The dry cell is rated at 1.5 Volts.
  6. An electron gains 2 electron volts of energy as it is transferred from point A to point B. What is the potential difference between A and B?
  7. An energy of 2.0 × 104 electron volts is equal to _____________