Question

In order to obtain a magnification of −2 (minus 2) with a concave mirror, the object should be placed:
(a) between pole and focus
(b) between focus and centre of curvature
(c) at the centre of curvature
(d) beyond the centre of curvature

Answer 1

We know that,

Magnification poduced by a spherical mirror = $m=\frac{h_2}{h_1}=-\frac{v}{u}$

$⟹m=-\frac{v}{u}=-2$

$⟹v=2u$

Using the mirror formula $\frac{1}{f}=\frac{1}{v}+\frac{1}{u}$ we get

$\frac{1}{f}=\frac{1}{2u}+\frac{1}{u}$

$⟹u=1.5f$

Thus, the object should be placed between focus and centre of curvature.

Hence option (b) is correct.