# Chapter 40 NATURE AND PROPOGATION OF LIGHT¶

## Example 40.1 Force and energy reﬂected¶

In [1]:
from __future__ import division
u=(10)*(1.0)*3600  #in Joules
c=3*10**8 #in m/sec
t=3600 #in sec
print("(A) Energy reflected from mirror in joule=",u)
p=(2*u)/c
print("Momentum after 1 hr illumination in kg-m/sec= %.5f"%p)
f=p/t
print("(B) Force in newton= %.3e"%f)

(A) Energy reflected from mirror in joule= 36000.0
Momentum after 1 hr illumination in kg-m/sec= 0.00024
(B) Force in newton= 6.667e-08


## Example 40.2 Angular speed¶

In [2]:
from __future__ import division
theta=1/1440
c=3*10**8 #in m/sec
l=8630 #in m
w=(c*theta)/(2*l)
print("Angular speed in rev/sec= %.5f"%w)

Angular speed in rev/sec= 12.07030


## Example 40.3 Calculation of c¶

In [3]:
from __future__ import division
l=15.6 #in cm
n=8
lambda_g=(2*l)/n
print("Lambda_g in cm=",lambda_g)
lamda=3.15  #in cm
f=9.5*10**9 #cycles/sec
c=lamda*f
print("Value of c in m/sec= %.3e"%c)

Lambda_g in cm= 3.9
Value of c in m/sec= 2.992e+10


## Example 40.4 Percentage error¶

In [4]:
from __future__ import division
v_1=25000 #miles/hr
u=25000   #miles/hr
c=6.7*10**8 #miles/hr
x=1+((v_1*u)/(c)**2)
v=(v_1+u)/x
print("Speed of light in miles/hour= %.0f"%v)

Speed of light in miles/hour= 50000