Question

If the focal length of the objective lens and the eye lens are 4 mm and 25 mm respectively in a compound microscope. The length of the tube is 16 cm. Find its magnifying power for relaxed eye position

• A. 32.75
• B. 327.5
• C. 0.3275
• D. None of the above

Answer 1

The correct option is B 327.5

The image distance for the objective, in this case, is $L-f_0-f_e$ as the focal lengths are not negligible compared to the length of the telescope.
By using $m_{\infty }=\frac{(L-f_0-f_e)D}{f_0{f}_e}$
$=\frac{(16-0.4-2.5)\times 25}{0.4\times 2.5}=327.5$