Question

(a) What does by magnifying power of a Microscope?
(b) An object is placed ar $20cm$ from a convex lens. If $3times$ magnified real image is formed by the lens then find the focal length of lens.

Answer 1

(a) Magnifying Power : The magnifying power of a simple microscope is defined as the ratio of the angles subtended by the image & the object at the eye, when both are at the least distance of distinct vision from the eye.
$Magnifyingpower=\frac{Anglesubtendedbytheimageattheleastdistanceofdistinctvision}{Angflesubtendedbytheobjectattheleastdistanceofdistinctvision}$
$\left(b\right)$ $m=\frac{f}{f+4}$ For real image $m=-3;u=-20$
$-3=\frac{f}{f-20}$
$-3f+60=f$
$4f=60$
$f=15cm$