Question

The given figure shows image formation by a lens. Analyse the figure and answer the following questions:

1. What is the type of lens used for image formation in the given ray diagram?
2. If the real image is formed at a distance of 30 cm from the lens and the size of image is twice the size of the object, then where was the object placed?

Answer 1

a. The lens in the diagram is a concave lens.

b. Given: Image is real, so it is on the opposite side (v) = 30 cm

Magnification (|m|) = 2    ...[Size is twice]

Since the image is real, it must be inverted, so m = −2.

By using the magnification formula for the lens:

m = `v/u`

−2 = `30/u`

u = `30/-2`

= −15 cm

∴ The object was placed at a distance of 15 cm in front of the lens.