Problem 10.7. Moon light passes through a converging lens of focal length 19 cm, which is 20.5 cm from a second converging lens of focal length 2 cm. Where is the image of the moon produced by the lens combination?
Data
Focal length of first lens f1 =19cm
Focal length of 2nd lens f2= -2cm
Distance between two lens 20.5cm
To find Image distance q =?
Solution
Images distance q1 formed by first lense Is given by
1/q1= 1/f1 - 1/p1 = 1/199 +1/infinity =1/19+0
Q1 = 19cm
Similarly For 2nd lens p2 can be found by L= q1+p2
P2= L-q1
20.5 -19 =1.5cm
And image distances formed by 2nd lens q2 is given by 1/q2 = 1/f2 - 1/p2
1/q2 = 1/2 - 1/1.5 = 1.5 - 2 /2× 1.5 = _0.5 / 3
20.5 - 6 = 14..5cm
