1. Fields in Parallel Plates-Capacitors
Physics Mr. Berman

2. Electric Fields Between Parallel Plates
Uniform Electric
Field of Strength:
E = V / d
d is the distance between the plates
Units: V/m =N/C=J/(Cm)

3. Force Experienced by a Test Charge Inside the Parallel Plate Field
The field is uniform so at any point in the field a test charge would feel a force
F = qE

4. Work and Energy V=Ed V=W/q0 W/q0= Ed W=q0 Ed
Unit for work: Joule or the electron volt
1 eV= qe 1V= 1.6 x 10-19C x 1V
1eV= 1.6 x 10-19J

5. Problem 1 Find: a)The field inside the plates.
b)The force felt by a 9nC charge
that is situated in the field.
120N/C, 10.8 x 10 **-7 N

6. Continued c)Draw the equipotential surfaces
between the plates (hint: equally
spaced and parallel)
d)If there three equipotential
surfaces,what would be the
distance between each?
e)The work to move the charge
from one equipotential to the other.

7. Continued
f)The potential difference between each equipotential surface and the negative plate.

8. Equipotentials and Field Lines

9. Equipotentials and Field Lines

10. Equipotentials and Field Lines

11. Note
Zero work is done when a charge is moved along an equipotential surface.

12. Milikan’s Oil Drop Experiment
He found the charge of the electron e = x C by noting that the droplets always carried whole number multiples of that number.

13. Capacitor

14. A capacitor stores charge (stores energy).

15. Capacitors

16. Leyden Jar 1746, Dutch physicist Pieter Van Musschenbroek
Lived in “Leyden”
Used by Ben Franklin

17. Capacitance Capacitance C = Q/V Unit: Farad (F)= coulomb/ volt
Q charge stored in capacitor
V voltage across the capacitor

18. Problem
What is the charge of a 2µC capacitor that is charged, so that the potential difference is 8V?

19. Question
If the charge of a capacitor is changed, does that affect the potential difference or the capacitance?