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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?
Solution
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.
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