Transcript Chapter 25

Chapter 25 Capacitors and Dielectrics
part(I)
Definition of capacitance:
C = Q/V
Measures the ability of a device to store charge
and electric energy.
The capacitance for different geometries:
A sphere:
C = 4 p eo R
Coaxial cylinders:
C = l [2k ln(b/a)]-1
Two concentric spheres:
C = ab/[k (b-a)]
Parallel plates:
C = eo A/d
Chapter 25 Capacitors and Dielectrics
part(II)
Equivalent Capacitors in series:
Cs-1 = C1-1 + C2-1 + C3-1 + ...
Equivalent Capacitors in parallel:
Cp = C1 + C2 + C3 + ...
Energy stored in a capacitor:
ue = eo E2/2
U = QV/2 = CV2/2 = Q2/(2C)
Effect of dielectric:
C = k Co
Battery not connected:
Q = Qo ; V = Vo/k ; U = Uo/k
Battery connected:
Q = k Qo ; V = Vo; U = k Uo