Question

An erect image `3 times` the size of the object is obtained with a concave mirror of radius of curvature `36 cm`. What is the position of the object ?

Answer 1

Here, `m = + 3` (because image is erect)
`R = -36 cm, u = ? Let u = -x`
As `m = (h_2)/(h_1) = (+ v)/(-u) = 3 :. v = -3 u = 3 x`
As `(1)/(u)+(1)/(v)=(1)/(f)=(2)/( R) :. (1)/(-x)+(1)/(3x)=(2)/(-36)`
`(-3 + 1)/(3x) = - (1)/(18)` or `3x = 36 :. x = 12 cm`
`:. u = -12 cm`.