Q: A point source of light is located 20 cm in front of a convex mirror with f = 15 cm. Determine the position and nature of the image point.

Sol: $\large \frac{1}{v} + \frac{1}{u} = \frac{1}{f} $

Here u = – 20 cm, f = 15 cm

$\large \frac{1}{v} = \frac{1}{f} – \frac{1}{u} $

$\large \frac{1}{v} = \frac{1}{15} – \frac{1}{-20} = \frac{35}{300}$

$\large \frac{1}{v} = \frac{7}{60} $

v = 8.6 cm

Also v is positive, the image is located behind the mirror.