1. Electric Potential Energy and the
Chapter 19
Electric Potential Energy and the
Electric Potential

2. 1) Electric Potential Energy

3. 2) Electric Potential

4. 3) Point Charges If V = 0 at r = ∞, then V r q
Superposition: potentials add as scalars q1 q2

5. 4) Equipotential surfaces
Definition
Surface with constant potential
e.g. For a point charge,
equipotential surfaces are spheres

6. e.g. parallel plates
E is uniform, and W = qEs, so
equipotential surfaces are planes

7. b) Work along an equipotential surface

8. E is perpendicular to equipotential surfaces
c) Electric field direction and equipotential surfaces
If W = 0, and E ≠ 0, then
E is perpendicular to equipotential surfaces

10. Electric field lines
Equipotential lines

11. d) Electric field as a potential gradient
units: V/m = J/(Cm) = N/C

12. In general,
Electric field points in the direction of maximum change of the potential

13. 5) Biomedical examples a) Conduction of electrical signals in neurons
Resting state (selective
permeability)
V=-70mV

14. Stimulated cell
Signal travels at ~ 50 m/s

15. b) Medical diagnostics
- body is not an equipotential surface
- Flow of Na+, K+, Cl- ions; potential differences ~ µV
- depend on stimuli and can form regular patterns

16. - heartbeat (electrocardiography, ECT, EKG)

17. - brain waves (electroencephalography, EEG)

18. - response to light (electroretinography, ERG)