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?

The simple microscope has magnification of 5 for normal relaxed eye (D = 25 cm).

Because the eye is relaxed the image is formed at infinity (normal adjustment).

So, $m=5\frac{D}{f}=\frac{25}{f}$

$\Rightarrow$ f= 5 cm

For the relaxed far sighted eye, D = 40 cm

So, $m=\frac{D}{f}=\frac{40}{5}=8$

So, its magnifying power is 8.