# Chapter 12 :Electricity¶

## Example 12.7 , Page no:70¶

In :
import math
from __future__ import division

#initialisation of variables
e=1.6*10**-19; #charge on an electron in coulomb
q=10**-12; #charge on pith ball in coulomb

#CALCULATIONS
n=q/e; #calculating no of electrons

#RESULTS
print"No. of electrons =",round(n,3);

No. of electrons = 6250000.0


## Example 12.8 , Page no:70¶

In :
import math
from __future__ import division

#initialisation of variables
k=9*10**9; #constant in free space in N.m square/C square
q1=4*10**-9; #charge in coulomb
q2=5*10**-8; #charge in coulomb
r=5*10**-2; #radius in metre

#CALCULATIONS
F=(k*q1*q2)/(r*r); #calculating force in Newton

#RESULTS
print"Force in Newton =",round(F,5);

Force in Newton = 0.00072


## Example 12.9 , Page no:71¶

In :
import math
from __future__ import division

#initialisation of variables
k=9*10**9; #constant in free space in N.m square/C square
q1=1.6*10**-19; #charge in coulomb
q2=1.6*10**-19; #charge in coulomb
r=5.3*10**-11; #radius in metre

#CALCULATIONS
F=(k*q1*q2)/(r*r); #calculating force in Newton

#RESULTS
print"Force in Newton =",'%.3E'%F;

Force in Newton = 8.202E-08


## Example 12.10 , Page no:71¶

In :
import math
from __future__ import division

#initialisation of variables
q1=5*10**-7; #charge in coulomb
q2=2*10**-7; #charge in coulomb
k=9*10**9; #constant in N.m square/coulomb square
F=10**2; #force in Newton

#CALCULATIONS
r=math.sqrt((k*q1*q2)/F); #calculating r using Coulomb's law
r1=r*10**3;

#RESULTS
print"Distance between them in mm =",round(r1,3);

Distance between them in mm = 3.0


## Example 12.12 , Page no:71¶

In :
import math
from __future__ import division

#initialisation of variables
k=9*10**9; #constant in N.m square/kg square
G=6.67*10**-11; #universal gravitational constant in N.m square/kg square
m1=1.67*10**-27; #mass in kg
m2=1.67*10**-27; #mass in kg
mp=1.6*10**-19; #mass of proton in kg

#CALCULATIONS
Fg=G*m1*m2;
Fe=k*mp*mp;
d=Fe/Fg;

#RESULTS
print"Times electric force is greater than gravitational force =",'%.3E'%d;

Times electric force is greater than gravitational force = 1.239E+36


## Example 12.13 , Page no:71¶

In :
import math
from __future__ import division

#initialisation of variables
F=8.2*10**-8; #force in Newton
e=1.6*10**-19; #charge on an electron in Coulomb

#CALCULATIONS
E=F/e; #calculating electric field in V/m using E=F/Q

#RESULTS
print"Electric field in v/m =",'%.3E'%E;

Electric field in v/m = 5.125E+11


## Example 12.14 , Page no:71¶

In :
import math
from __future__ import division

#initialisation of variables
e=1.6*10**-19; #charge on an electron in coulomb
E=5*10**3; #electric field in V/m
m=3.3*10**-26; #mass of neon ion in kg

#CALCULATIONS
F=E*e; #calculating foece in Newton using F=Q*E
a=F/m; #calculating accelaration in m/sec square using Newton's Law(F=m*a)

#RESULTS
print"Force on neon Ion in Newton =",'%.3E'%F;
print"Accelaration of the ion in m/sec square =",'%.3E'%a;

Force on neon Ion in Newton = 8.000E-16
Accelaration of the ion in m/sec square = 2.424E+10


## Example 12.15 , Page no:72¶

In :
import math
from __future__ import division

#initialisation of variables
m=1.67*10**-27; #mass of proton in kg
g=9.8; #gravitational constant in m/sec square
e=1.6*10**-19; #charge on electron in coulomb

#CALCULATIONS
E=(m*g)/e; #calculating Electric field in V/m using e*E=m*g

#RESULTS
print"Electric Field in V/metre =",round(E,7);

Electric Field in V/metre = 1e-07


## Example 12.16 , Page no:72¶

In :
import math
from __future__ import division

#initialisation of variables
Q=50; #charge in Coulomb
V=7*10**6; #Potential difference in Volt

#CALCULATIONS
W=Q*V; #calculating energy dissipated in Joule

#RESULTS
print"Power dissipated in Joule =",'%.3E'%W;

Power dissipated in Joule = 3.500E+08


## Example 12.17 , Page no:72¶

In :
import math
from __future__ import division

#initialisation of variables
V=20; #potential difference in Volt
E=500; #Electric field in V/m

#CALCULATIONS
s=V/E; #calculating distance between them in metre using s=V/E
s1=s*100;

#RESULTS
print"Distance between the plates in metre =",round(s,3);
print"Distance between the plates in cm =",round(s1,3);

Distance between the plates in metre = 0.04
Distance between the plates in cm = 4.0


## Example 12.18 , Page no:72¶

In :
import math
from __future__ import division

#initialisation of variables
E=600; #electric field in volt/metre
s=0.15; #distance between plates in metre
r=0.05; #distance in m
Q=10**-10; #charge in coulomb

#CALCULATIONS
V=E*s; #calculating potential difference in Volt
F=Q*E; #calculating force in Newton
KE=F*r; #calculating Kinetic Energy in Joule

#RESULTS
print"(a)Potential Difference in Volt =",round(V,3);
print"Force on the charge of 10^-10 C in Newton =",F;
print"Kinetic Energy in Joule =",KE;

(a)Potential Difference in Volt = 90.0
Force on the charge of 10^-10 C in Newton = 6e-08
Kinetic Energy in Joule = 3e-09


## Example 12.19 , Page no:73¶

In :
import math
from __future__ import division

#initialisation of variables
m=9.1*10**-31; #mass of electron in kg
v=10**7; #velocity of electron in m/sec
e=1.6*10**-19; #charge on electron in coulomb

#CALCULATIONS
KE=(1/2)*(m*v*v); #Kinetic Energy of electron in Joule
V=KE/e; #calculating potential difference in Volt

#RESULTS
print"Kinetic Energy in Joule =",'%.3E'%KE;
print"Potential difference in Volt =",round(V,3);

Kinetic Energy in Joule = 4.550E-17
Potential difference in Volt = 284.375


## Example 12.20 , Page no:73¶

In :
import math
from __future__ import division

#initialisation of variables
V=12; #potential diff in volt
Q=15; #charge per time in Coulomb/sec
t=3600; #time (seconds in an hour)

#CALCULATIONS
P=V*Q; #calculating power in Watt
W=P*t; #work done in Joule

#RESULTS
print"Power in Watt =",round(P,3);
print"Work done in 1 hr in Joule =",round(W,3);

Power in Watt = 180.0
Work done in 1 hr in Joule = 648000.0