Question

An object is to be seen through a simple microscope of power 10 D. Where should the object be placed to reduce maximum angular magnification? The least distance for distinct vision is 25 cm.

(a) + 7.1 cm

(b) – 7.1 cm

(c) + 25 cm

(d) – 25 cm

I have been asked this question in a job interview.

The doubt is from Optical Instruments topic in portion Ray Optics and Optical Instruments of Physics – Class 12

Answer 1

Correct choice is (b) – 7.1 cm

Explanation: Angular magnification is maximum when the final image is formed at the near point.

\(\frac {1}{u} = \frac {1}{v} – \frac {1}{f}\)

\(\frac {1}{u} = ( \frac {-1}{25} ) – ( \frac {1}{10} ) \)

u = -7.1 cm.

Therefore, the object should be placed 7.1 cm before the lens to avoid angular magnification.