Chapter 15 : Electric forces and electric fields

Example 15.1 Page No : 502

In [1]:
k_e=8.99*10**9
e=1.6*10**-19
r=5.3*10**-11
F_e= (k_e*e*e)/(r*r)
print "The attractive force = %0.2e N"%F_e
G=6.67*10**-11
m_e=9.11*10**-31
m_p=1.67*10**-27
F_g=(G*m_e*m_p)/(r*r)
print "The gravitational force = %0.2e N"%F_g

The attractive force = 8.19e-08 N
The gravitational force = 3.61e-47 N

Example 15.2 Page No : 503

In [2]:
k_e=8.99*10**9 #N.m**2/c**2
q2=2*10**-9# = %0.2f c
q3=5*10**-9# = %0.2f c
r1=4#in m
F_23=(q2*q3*k_e)/(r1*r1)
print "The force = %0.2e N"%F_23
q1=6*10**-9
r2=5#in m
F_13=(q1*q3*k_e)/(r2*r2)
print "The force = %0.2e N"%F_13

The force = 5.62e-09 N
The force = 1.08e-08 N

Example 15.4 Page No: 507

In [3]:
q=1.6*10**-19#in c
E=2*10**4# = %0.2f N/C
F=q*E
print "The magnitude of force = %0.2e N"%F

The magnitude of force = 3.20e-15 N

Example 15.5 Page No: 509

In [4]:
from math import degrees, atan
k_e=8.99*10**9 #N.m**2/c**2
q1=7*10**-6# = %0.2f C
q2=5*10**-6#in C
r1=0.4
r2=0.5
E1=(k_e*q1)/(r1**2)
E2=(k_e*q2)/(r2**2)
Ex=(k_e*q2)/(r2**2)
print "Magnitude of E1 = %0.2e N/C"%E1
print "Magnitude of E2 = %0.2e N/C"%E2
print "Magnitude in x direction = %0.2e N/C"%Ex
Ey=(3.93*10**5)+(-1.44*10**5)
print "Magnitude in y direction = %0.2e N/C"%Ey
phi=degrees(atan(Ey/Ex))
print "Angle = %0.2f degree"%phi
#Answer given in the book is wrong

Magnitude of E1 = 3.93e+05 N/C
Magnitude of E2 = 1.80e+05 N/C
Magnitude in x direction = 1.80e+05 N/C
Magnitude in y direction = 2.49e+05 N/C
Angle = 54.17 degree