1. Electrical Energy and Potential Difference

2. When two charges interact, there is a force between them
When two charges interact, there is a force between them. This force creates potential energy.
This electric PE is a form of mechanical energy, like KE, GPE and PEelastic

3. - - Charges moving in a uniform electric field + +
A + charge moving against the electric field gains PE
A + charge moving with the electric field loses PE
A - charge moving against the electric field loses PE
A - charge moving with the electric field gains PE

4. DPEelectric = -qEDd Measured in Joules
Dd is in the direction of the electric field

5. Electrical Potential Energy for a pair of charges

6. Electric Potential is the amount of PEelectric divided by the amount of charge
Potential Difference is the change in V

7. Potential Difference is measured in Volts (V), which equals 1 J/C
It can also be expressed as DV = -EDd or DV = kCq/r or DV = W/q

8. Sample Problems
A uniform electric field is directed in the + x direction at 250 N/C. A 12mC charge moves from the origin to the point (20.0 cm, 50.0 cm). What is the change in PE?
Given
DPEelectric = -qEDd
q = 12 x 10-6 C
= (-12 x 10-6 C)(250 N/C)(.200 m)
moving with field, so will lose PE
= -6.0 x 10-4 J
E = 250 N/C
d = .200 m

9. A proton is released from rest in a uniform electric field of 8
A proton is released from rest in a uniform electric field of 8.0 x 104 V/m and moves .50 m. Find the potential difference and DPE for these positions.
Given a)
DV = -EDd
E = 8.0 x 104 V/m
DV = -(8.0 x 104 V/m)(.5 m)
d = .5 m
DV = -4.0 x 104 V b)
DPE = DVq
q = 1.60 x C
DPE = (-4.0 x 104 V)(1.60 x C)
DPE = -6.4 x J