1. ELECTRIC ENERGY AND ELECTRIC POTENTIAL

2. ENERGY REVIEW When we studied energy a couple of months ago there were a few major points of interest: Work is a change in energy that one object gave to another object. Kinetic Energy is moving energy. Potential Energy is stored energy. Kinetic energy can turn into Potential Energy and vice versa.

3. ELECTRIC POTENTIAL ENERGY Earlier in the year we looked at two different types of Potential Energy: Gravitational and Elastic/Spring. For Gravitational Potential Energy, the work done by the gravity field on the object was equal to the negative work done by the external force causing the displacement of the object. Example: Lifting a box in a gravity field Work done by external force: W = mgh Work done by gravity field: W = -mgh

4. ELECTRIC POTENTIAL ENERGY

5. POTENTIAL ENERGY DUE TO A FIELD A test charge moving through an electric field can be treated just like a ball moving through a gravity field. Positive Charge Negative Charge Positive Charge + -

6. POTENTIAL ENERGY DUE TO CHARGES If two charges have the SAME sign, the Electric Potential Energy is POSITIVE since it takes POSITIVE WORK by an external force to bring them together. If two charges have DIFFERENT signs, the Electric Potential Energy is NEGATIVE since it takes NEGATIVE WORK by an external force to bring them together. Think of this like you would a spring. If these two charges were released from their positions, they would fly apart due to the stored potential energy. ++

7. ANOTHER WAY TO THINK OF IT… Since the charge would naturally want to go down (towards the negative charge) it would require work to move it up. If I do POSITIVE work to the charge, it would GAIN potential energy.

8. ELECTRIC POTENTIAL Electric Potential – A scalar characteristic of an electric field, independent of any charges that may be placed in the field. Essentially, Electric Potential (or Potential for short) is Electric Potential Energy without the charge. Electric Potential only describes the field. Only Source ChargeSource and Test Charge Electric FieldElectric Force Electric PotentialElectric Potential Energy

9. ELECTRIC POTENTIAL Electric Potential Test Charge Source Charge Distance Electric Field Work

10. THE ELECTRON VOLT Electron Volt (eV) – the energy a charge-field system gains or loses when a charge of 1 electron is moved through a potential difference of 1 Volt. 1 eV = 1.6 x 10 -19 J

11. POTENTIAL DIFFERENCE IN A FIELD Potential Difference is the change in the amount of Electric Potential between two different locations. Another name for Potential Difference is Voltage. Initial Potential Final Potential Potential Difference = Final Potential – Initial Potential Arrows ALWAYS point toward the area with a lower potential.

12. POTENTIAL DIFFERENCE This is how a battery makes a circuit work! The battery creates a potential difference in the wires, therefore moving the electrons through the wire…

13. POTENTIAL DUE TO A SOURCE CHARGE r1r1 r2r2 q1q1 q2q2

14. PRACTICE PROBLEM A charge of 3 x 10 -6 C is located 0.1 m to the left of the origin and a charge of - 4.0 x 10 -6 C is located 0.1 m to the right of the origin. Where is the electric potential equal to zero between them?