Question

An optical instrument uses a lens of power 100 D for objective lens and 50 D for its eyepiece. When the tube length is kept at 25 cm. the final image is formed at infinity.

1. Identify the optical instrument
2. Calculate the magnification produced by the instrument.

Answer 1

a. The instrument is called a compound microscope.

b. Power of objective (P_O) = 100 D

∴ f_O = `1/100` m

= 1 cm

Power of eyepiece (P_E) = 50 D

∴ f_E = `1/50` m

= 2 cm

Length of tube (L) = 25 cm

Least distance of distinct vision (D) = 25 cm

Magnification = `25/1 xx 25/2`

= 312.5