Question

The focal lengths of the objective and the eye-piece of a compound microscope are 2.0 cm and 3.0 cm respectively. The distance between the objective and the eye-piece is 15.0 cm. The final image formed by the eye-piece is at infinity. The two lenses are thin. The distances in cm of the object and the image produced by the objective measured from the objective lens are respectively –

• A. 2.4 and 12.0
• B. 2.4 and 15.0
• C. 2.3 and 12.0
• D. 2.3 and 3.0

Answer 1

Answer: (A)

2.4 and 12.0

Answer 2

When final image is formed at  length of tube = v₀ + f_e Ž 15 = v₀ + 3

Ž v₀ = 12 cm

For objective lens

$\frac { 1 } { \mathrm { f } _ { 0 } }$ = –

$\frac { 1 } { + 2 }$ = $\frac { 1 } { + 12 }$ – Ž $\mathrm { u } _ { 0 } = - 2.4 \mathrm {~cm}$