Question

An object is placed on the principal axis of a concave mirror at a distance of 1.5 f (f is the focal length). The image will be at,

(1) 3f

(2) –3f

(3) 1.5 f

(4) –1.5f

Answer 1

-1/f= 1/v - 1/u

-1/f + 1/1.5f = 1/v 

-1.5f+f/1.5f² = 1/v 

1/v = -3

Answer 2

-1/f=1/v-1/u

-1/f+1/1.5f=1/v

-1/f+1/3f/2=1/v

-3+2/3f=1/v

-1/3f=1/v

V=-3f