Chapter 1 Coulombs Law

Example 1.1 Page no 12

In [2]:
#Given
q=-3*10**-7                          #C
e=-1.6*10**-19                      #C

#Calculation
n=q/e

#Result
print"Number of electrons transferred from wool to polythene is", n

Number of electrons transferred from wool to polythene is 1.875e+12

Example 1.2 Page no 12

In [23]:
#Given
m=3.11                #g
Z=29
A=63.5 
N=6.023*10**23
e=1.6*10**-19

#Calculation
n=(N*m)/A
n1=n*Z
q=n1*e

#Result
print"Total positive or negative charge is", round(q*10**-5,2),"*10**5 C"

Total positive or negative charge is 1.37 *10**5 C

Example 1.3 Page no 12

In [11]:
#Given
q1=2*10**-7
q2=3*10**-7
r=0.3                        #m
a=9*10**9

#Calculation
F=(a*q1*q2)/r**2

#Result
print"Force between two small charged spheres is", F*10**3,"*10**-3","N(repulsive"

Force between two small charged spheres is 6.0 *10**-3 N(repulsive

Example 1.4 page no. 12

In [16]:
#Given
F=3.7*10**-9                         #N
r=5*10**-10                           #m
a=9*10**9
q1=1.6*10**-19

#Calculation
import math
n=math.sqrt(F*r**2/(a*q1**2))

#Result
print"number of electrons is", round(n,0)

number of electrons is 2.0

Example 1.5 Page no 12

In [32]:
#Given
q1=0.4*10**-6                       #C
q2=0.8*10**-6                       #C
F12=0.2                               #N
a=9.0*10**9

#Calculation
import math
r=math.sqrt((a*q1*q2)/F12)

#Result
print"(a) Distance between two spheres is", r,"m"
print"(b) Force on charge q2 due to q1 is",F12,"N"

(a) Distance between two spheres is 0.12 m
(b) Force on charge q2 due to q1 is 0.2 N

Example 1.6 Page no 13

In [40]:
#Given
q1=5*10**-8                                  #C
m1=8*10**-3                                       #Kg
a=9*10**9
r=0.05                                             #m

#Calculation
q2=m1*9.8*r**2/(a*q1)

#Result
print"Charge q2 is", round(q2*10**7,2)*10**-7,"C(positive)"

Charge q2 is 4.36e-07 C(positive)

Example 1.7 Page no 13

In [57]:
#Given
q1=6.5*10**-7                              #C
q2=6.5*10**-7
r=0.5                                    #m
a=9*10**9
K=80.0

#Calculation
Fair=a*q1*q2/r**2
r1=0.5/2.0
F1=a*4*q1*q2/r1**2
Fwater=Fair/K

#Result
print"(a) Mutual force of electrostatic repulsion is", Fair*10**2,"*10**-2 N"
print"(b) (i) Force of repulsion is", round(F1,4),"N"
print "(ii) Force of repulsion is",round(Fwater*10**4,1),"*10**-4 N"

(a) Mutual force of electrostatic repulsion is 1.521 *10**-2 N
(b) (i) Force of repulsion is 0.2434 N
(ii) Force of repulsion is 1.9 *10**-4 N

Example 1.8 Page no 13

In [64]:
#Given
q1=6.5*10**-7                       #C
r=0.05                              #m
a=9*10**9
r1=0.5

#Calculation
q11=q1/2.0
q21=(q1+q11)/2.0
F=(a*q11*q21)/r1**2

#Result
print"New force of repulsion between A and B is", round(F*10**3,3),"*10**-3 N"

New force of repulsion between A and B is 5.704 *10**-3 N

Example 1.10 Page no 14

In [100]:
#Given
a=9.0*10**9
r=0.2
m=9.8*10**-3
a1=0.1
a2=0.5

#Calculation
import math
a11=m*(a1/(math.sqrt(a2**2-a1**2)))
q=math.sqrt((a11*r**2)/a)

#Result
print"Charge on each ball is", round(q*10**8,2)*10**-6,"C"

Charge on each ball is 9.43e-06 C

Example 1.12 Page no 14

In [75]:
#Given
qa=10**-5                             #C
qb=5*10**-6                           #C
qc=-5*10**-6                          #C
r=0.1                                 #m
a=9*10**9

#Calculation
import math
Fab=(a*qa*qb)/r**2
Fac=Fab
F=math.sqrt(Fab**2+Fac**2+(2*Fab*Fac*math.cos(120*3.14/180.0)))

#Result
print"Resultant force is", round(F,0),"N"

Resultant force is 45.0 N

Example 1.13 Page no 15

In [90]:
#Given
qa=1
qb=100
ab=10
a=9*10**9
qd=75
a1=5

#Calculation
import math
Fab=(a*qa*qb)/ab**2
Fac=Fab
Fac1=(a*qa*qd)/(ab**2-a1**2)
Fx=Fab*math.cos(60*3.14/180.0)+Fac1*math.cos(60*3.14/180.0)
Fy=Fac
F=math.sqrt(Fx**2+Fy**2)
B=Fy/Fx
B1=math.atan(B)*180/3.14

#Result
print"Resultant force on charge qa is inclined at", round(B1,0),"Degree"

Resultant force on charge qa is inclined at 45.0 Degree