Question

8. An object is placed at a distance of 20 cm forin a convex inirror. The image forms at a distance of 12 cm from the mirror: l'ind the focal length of the mirror [Ans. 30 cm]​

Answer 1

apply the formula

$1 \div f = 1 \div u + 1 \div v$

where f is focal length

u is object distance

v is image distance.

GIVEN:

u = -20cm

v = +12cm

f = ?

1/f = 1/12 + (-1/20)

= 1/12 - 1/20

= 1/30

then

f = 30cm