Question

An object is held in front of conacve mirror of focal length `15 cm`. The image formed is `3` times the size of the object. Calculate two possible distances of the object from the mirror.

Answer 1

Correct Answer - `-10 cm`; `-20 cm`
Here, `f = - 15 cm, m = +- 3, u = ?`
As `m = -(v)/(u) = + 3, v = - 3 u`
From `(1)/(v) + (1)/(u) = (1)/(f)`, `(1)/(-3u) + (1)/(u) = (1)/(-15)`
or `(2)/(3 u) = (1)/(-15)`, `u = -10 cm`
Similarly, when `m = -(v)/(u) = - 3`, we get
`u = - 20 cm`