Question

real image formed by a concave mirror is 4.5 times the size of an object if the if the mirror is 20 centimetre from the object its focal length is ________​

Answer 1

Explanation:

magnification m = - v / u = -4 (given)

v is mirror to image distance; u is mirror to object distance = -20 (by sign convention)

hence v = -80 cm

we have mirror equation, begin mathsize 12px style 1 over v space plus space 1 over u space equals space 1 over f end style

hence (-1/80)+(-1/20) = (-5/80) , f = -16 cm