# Chapter 23:Optical Devices¶

## Ex23.1:pg-1094¶

In [1]:
  #Example 23_1
import math

#To find the focal length of the reading glasses
d1=25.0       #units in cm
d2=-75        #units in cm
f=(d1*d2)/(d2+d1)     #Units in cm
print "The focal length of the reading glasses is f=",round(f,2)," cm"

The focal length of the reading glasses is f= 37.5  cm


## Ex23.2:pg-1094¶

In [2]:
  #Example 23_2
import math

#To find the focal length of the corrective lens
d1=-50.0           #units in cm
f=-(d1)         #Units in cm
print "The focal length of the corrective lens is f=",round(f)," cm"

The focal length of the corrective lens is f= 50.0  cm


## Ex23.3:pg-1095¶

In [3]:
  #Example 23_3
import math

#To find the focal length of the combination
d1=20.0            #units in cm
d2=-30.0             #units in cm
d3=60.0           #units in cm
p1=100/d1         #units in dipoters
p2=100/d2         #units in dipoters
p3=100/d3         #units in dipoters
p=1/(p1+p2+p3)          #Units in diopters
print "The combined focal length is=",round(p,1)," cm"

The combined focal length is= 0.3  cm