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.