In [1]:

```
import math
#Given Data:
lamda=694.3*10**-9 #Wavelength in meter
T=300 #Temperature in Kelvin
h=6.63*10**-34 #Planck's Constant
c=3*10**8 #Velocity of light
K=1.38*10**-21 #Boltzmann Constant
#Calculations:
delE= h*c/lamda #Energy difference between two energy states N and N0
#N=N0*e^-delE/(K*T)
R=math.e**(-delE/(K*T)) #R=Ratio of N and N0 i.e.(R=N/N0)
#(Printing mistake in textbook)
#instead of e^-.692, it has taken e^-69.2
print"The ratio of population of two energy states is = ",R
print" (calculation mistake in book)"
```

In [3]:

```
import math
#Given Data:
lamda=6328*10**-10 #Wavelength in meter
P=4.5*10**-3 #Power in watts
h=6.63*10**-34 #Planck's Constant
c=3*10**8 #Velocity of light
#Calculations:
delE= h*c/lamda #Energy difference
#N*delE=P
N=P/delE #number of photons emitted per second
print"Number of photons emitted per second is =",N
```

In [6]:

```
import math
#Given Data:
lamda=780*10**-9 #Wavelength of photon in meter
P=20*10**-3 #Power of each pulse in watts
t=10*10**-9 #Duration of each pulse
h=6.63*10**-34 #Planck's Constant
c=3*10**8 #Velocity of light
#Calculations:
delE= h*c/lamda #Energy of each photon
E=P*t #Energy of each pulse
N=E/delE #Number of photons in each pulse
print"Number of photons in each pulse is =",N
```

In [ ]:

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```