The focal length of the objective and the eyepiece of a microscope are 4 mm and 25 mm respectively. If the final image is formed at infinity and the length of the tube is 16 cm, then the magnifying power of microscope will be

Question

The focal length of the objective and the eyepiece of a microscope are 4 mm and 25 mm respectively. If the final image is formed at infinity and the length of the tube is 16 cm, then the magnifying power of microscope will be (A) -337.5 (B) -3.75 (C) 3.375 (D) 33.75

Tardigrade Admin · Accepted Answer

When final image is formed at ∞, then M=(vo/uo)((d/fe))=(vo/fo)((d/fe)) Now, vo=16-f e =16-2.5=13.5 cm ∴ M=(13.5/-0.4) × (25/2.5)=-337.5

Q. The focal length of the objective and the eyepiece of a microscope are $4 mm$ and $25 mm$ respectively. If the final image is formed at infinity and the length of the tube is $16 c m$ , then the magnifying power of microscope will be

-337.5

-3.75

3.375

33.75

When final image is formed at $\infty$ , then
$M = \frac{v _{o}}{u _{o}} (\frac{d}{f _{e}}) = \frac{v _{o}}{f _{o}} (\frac{d}{f _{e}})$
Now, $v_{o} = 16 - f_{e} = 16 - 2.5 = 13.5 c m$
$∴ M = \frac{13.5}{- 0.4} \times \frac{25}{2.5} = - 337.5$

Q. The focal length of the objective and the eyepiece of a microscope are 4mm and 25mm respectively. If the final image is formed at infinity and the length of the tube is 16cm, then the magnifying power of microscope will be