When a concave mirror is placed facing the sun, the sun's rays converge to a point 10 cm from the mirror. Now if you place a 2 cm long candle flame 20 cm away on the principal axis of the mirror, where would you place a screen to obtain the image of the candle? What would be the size of the image? Draw a ray diagram to justify your answer.

Explanation

As sun's rays converge to a point 10 cm from the concave mirror, therefore, focal length of mirror `f = -(10) cm`. Now, `h_(1) = 2 cm, u = -20 cm , v = ?`
From `1/v + 1/u= 1/f`
`1/v = 1/f - 1/u = 1/(-10) - 1/(-20) = (-1)/20`
`v = -20 cm`
As `h_(2)/h_(1) = -v/u = -((-20)/(-20)) = -1`
`h_(2) = -h_(1) = -2 cm`.
Minus sign is for inverted image. The course of rays is as shown in Fig.
A'B' is real, inverted image of AB at C only.