11: Laser

Example number 11.1, Page number 246

In [2]:
#importing modules
import math
from __future__ import division

#Variable declaration
e=1.6*10**-19;     #charge(coulomb)
v=3*10**3;   #velocity of matter wave(m/s)
h=6.6*10**-34;    #plank's constant(Js)
lamda=600*10**-9;    #wavelength(m)

#Calculation
Ej=h*v/lamda;    #matter wave energy(J)
E=Ej/e;      #matter wave energy(eV)

#Result
print "matter wave energy is",round(E*10**5,2),"*10**-5 eV"
print "answer given in the book is wrong"

matter wave energy is 2.06 *10**-5 eV
answer given in the book is wrong

Example number 11.2, Page number 246

In [3]:
#importing modules
import math
from __future__ import division

#Variable declaration
e=1.6*10**-19;     #charge(coulomb)
c=3*10**10;   #velocity of light(m/s)
h=6.6*10**-34;    #plank's constant(Js)
Eg=3;    #energy gap(eV)

#Calculation
lamda=h*c*10**9/(Eg*e);     #wavelength of photon(nm)

#Result
print "wavelength of photon is",lamda,"nm"
print "answer given in the book is wrong"

wavelength of photon is 41250.0 nm
answer given in the book is wrong

Example number 11.3, Page number 246

In [4]:
#importing modules
import math
from __future__ import division

#Variable declaration
e=1.6*10**-19;     #charge(coulomb)
E2_E1=3*e;    #energy gap(J)
Kb=1.38*10**-23;    #boltzmann constant(J/K)
T=323;    #temperature(K)

#Calculation
n=math.exp(-E2_E1/(Kb*T));    #ratio in higher and lower energy

#Result
print "ratio in higher and lower energy is",round(n*10**47,4),"*10**-47"
print "answer given in the book is wrong"

ratio in higher and lower energy is 1.7081 *10**-47
answer given in the book is wrong

Example number 11.4, Page number 247

In [5]:
#importing modules
import math
from __future__ import division

#Variable declaration
c=2.998*10**8;     #velocity of light(m/s)
Kb=1.381*10**-23;    #boltzmann constant(J/K)
T=1000;    #temperature(K)
h=6.626*10**-34;    #plank's constant(Js)
lamda=0.5*10**-6;   #wavelength(m)

#Calculation
v=c/lamda;    #frequency(Hz)
BA=1/(math.exp(h*v/(Kb*T))-1);      #ratio of emission

#Result
print "ratio of emission is",round(BA*10**13,1),"*10**-13"
print "answer varies due to rounding off errors"

ratio of emission is 3.2 *10**-13
answer varies due to rounding off errors

Example number 11.5, Page number 247

In [6]:
#importing modules
import math
from __future__ import division

#Variable declaration
c=2.998*10**8;     #velocity of light(m/s)
h=6.626*10**-34;    #plank's constant(Js)
e=1.602*10**-19;     #charge(coulomb)
Eg=1.43;    #energy gap(eV)   

#Calculation
lamda=h*c*10**6/(Eg*e);        #wavelength(micro m)

#Result
print "wavelength is",round(lamda,2),"micro m"

wavelength is 0.87 micro m