Question

Find the position of the image in the following lens combination:

(a) 30 cm to the right of the third lens

(b) 20 cm to the right of the third lens

(c) 30 cm to the left of the third lens

(d) 20 cm to the left of the third lens

I got this question by my college director while I was bunking the class.

The origin of the question is Optical Instruments topic in portion Optics of Engineering Physics II

Answer 1

The correct answer is (a) 30 cm to the right of the third lens

To elaborate: Image by the first lens,

\(\frac{1}{V_1}-\frac{1}{U_1}=\frac{1}{f_1} \)

\(\frac{1}{V_1}-\frac{1}{-30}=\frac{1}{10}\)

v1 = 15 cm

For the second lens,

\(\frac{1}{V_2}\frac{-1}{-10}=\frac{1}{10}\)

 V2 = ∞

For the third,

\(\frac{1}{V_3}\frac{-1}{\infty}=\frac{1}{30}\)

V3 = 30 cm.