Question

An object of height 1.2 m is placed before a concave mirror of focal length 20 cm so that a real image is formed at a distance of 60 cm from it. Find the position of the object ? What will be the height of image formed ?

Answer 1

Here, `h_(1) = 1.2 m`, `f = -20 cm`
`v = -60 cm`, `u = ? h_(2) =?`
From mirror formula
`1/v + 1/u = 1/f`
`1/u = 1/f - 1/v = 1/(-20) + 1/60 = -1/30`
`u = -30 cm`
Therefore the object is to be held at 30 cm in front of the mirror.
As `h_(2)/h_(1) = (-v)/u = 60/(-30) = 2`
`:. h_(2) = -2h_(1) = -2 xx 1.2 m = -2.4 m`
Negative sign represents inverted image.