Question

If the focal length of the objective lens is increased, then the magnifying power of -

• A. compound microscope will increase, but that of telescope will decrease.
• B. both compound microscope and telescope will increase.
• C. both compound microscope and telescope will decrease.
• D. compound microscope will decrease, but that of telescope will increase.

Answer 1

The correct option is D compound microscope will decrease, but that of telescope will increase.

For a compound microscope, $m\propto \frac{1}{f_o}$ and for a telescope, $m\propto f_o$

Therefore, if the focal length of the objective lens is increased, then the magnifying power of compound microscope will decrease, but that of telescope will increase.

Hence, option $\left(D\right)$ is the correct answer.