Question

A point object is placed at a distance of 20 cm from a thin plano-convex lens of focal length 15 cm, if the plane surface is silvered. The image will form at:

Options

• 60 cm left of AB

• 30 cm left of AB

• 12 cm left of AB

• 60 cm right of AB

Answer 1

12 cm left of AB

Explanation:

lf f_e be the focal length of the lens, then

`1/"f"_"e" = 2/15 + 1/∞`

or f_e = 7.5 cm

Now using the mirror formula, we have

`1/"v" + 1/(-20) = 1/(-7.5)`

∴ v = −12 cm