Question

A simple microscope is rated 5 X for a normal relaxed eye. What will be its magnifying power for a relaxed farsighted eye whose near point is 40 cm?

Answer 1

For a simple microscope,
Magnification for a normal relaxed eye, m = 5
Least distant of distinct vision, D = 25 cm
Now,
Let the focal length be f.
The image will form at infinity, as the eye is relaxed.
The magnifying power  (m) of a simple microscope in normal adjustment is given by

`m =D/f`

`=> 5 = 25/f`

⇒ f= 5 cm

For the relaxed far-sighted eye, D = 40 cm.
Magnification (m):

`m=D/f =40/5 =8`

The magnifying power for a simple microscope is 8X.