# Chapter 30 CAPACITORS AND DIELECTRICS¶

## Example 30.1 Plate area¶

In [1]:
from __future__ import division
C=1.0 #capacitance in farad
d=1.0*10**-3 #separation b/w plates in meter
epsilon0=8.85*10**-12 #coul2/nt-m2
A=d*C/epsilon0
print("Plate area in square meter is %.3e"%A)

Plate area in square meter is 1.130e+08


## Example 30.5 To calculate Capacitance Free charge Electric ﬁeld strength Potential diﬀrence between plates¶

In [2]:
from __future__ import division
epsilon0=8.85*10**-12 #coul2/nt-m2
A=100*10**-4#area of the plate in square meter
d=1*10**-2 #separation b/w plates in meter
b=5*10**-3 #thickness of dielectric lab in meter
V0=100#in volts
k=7
#(a)
C0=epsilon0*A/d
print("(a)Capacitance before the slab is inserted in farad is %.3e"%C0)
#(b)
q=C0*V0
print("(b)Free charge in coul is %.3e"%q)
#(c)
E0=q/(epsilon0*A)
print("(c)Electric field strength in the gap in volts/meter is %d"%E0)
#(d)
E=q/(k*epsilon0*A)
print("(d)Electric field strength in the dielectric in volts/meter is %.4f"%E)
#(e)
#Refer to fig30-12
V=E0*(d-b)+E*b
print("(e)Potential difference between the plates in volts is %.4f"%V)
#(f)
C=q/V
print("(f)Capacitance with the slab in place in farads is %.3e"%C)

(a)Capacitance before the slab is inserted in farad is 8.850e-12
(b)Free charge in coul is 8.850e-10
(c)Electric field strength in the gap in volts/meter is 10000
(d)Electric field strength in the dielectric in volts/meter is 1428.5714
(e)Potential difference between the plates in volts is 57.1429
(f)Capacitance with the slab in place in farads is 1.549e-11


## Example 30.6 To calculate Electric displacement and Electric polarisation in dielectric and air gap¶

In [2]:
from __future__ import division
epsilon0=8.85*10**-12 #coul2/nt-m2
A=100*10**-4#area of the plate in square meter
d=1*10**-2 #separation b/w plates in meter
V0=100#in volts
E0=1*10**4 #Electric field in the air gap in volts/meter
k=7
k0=1
E=1.43*10**3 #in volts/metre
D=k*E*epsilon0
P=epsilon0*(k-1)*E
#(a)
print("(a)Electric displacement in dielectric in coul/square metre is %.3e"%D)
print("Electric polarisation in dielectric in coul/square meter is %.3e"%P)
#(b)
D0=k0*epsilon0*E0
print("(b)Electric displacement in air gap in coul/square metre is %.3e"%D0)
P0=epsilon0*(k0-1)*E0
print("Electric polarisation in air gap in coul/square meter is",P0)

(a)Electric displacement in dielectric in coul/square metre is 8.859e-08
Electric polarisation in dielectric in coul/square meter is 7.593e-08
(b)Electric displacement in air gap in coul/square metre is 8.850e-08
('Electric polarisation in air gap in coul/square meter is', 0.0)