A point object is placed at a distance of 60 cm from a convex lens of a focal length of 30 cm. If a plane mirror were put perpendicular to the principal axis of the lens and at a distance of 40cm from it, the final image would be formed at a distance of -

By Shivank Goel|Updated : August 25th, 2022

1. 20 cm from the plane mirror, it would be a virtual image
2. 20 cm from the lens, it would be a real image
3. 30 cm from the lens, it would be a real image
4. 30 cm from the plane mirror, it would be a virtual image

Let us use the lens formula

1/v1 - 1/u = 1/f

Given

u = -60 cm

f = 30 cm

v1 = ?

For the first refraction from a convex lens

1/v1 + 1/60 = 1/30

So we get

v1 = 60 cm

l1 is the first image by the lens

An image will be produced by the plane image at a 20 cm distance to the left of it

For the second refraction from a convex lens

u = -20 cm

v = ?

f = 30 cm

Using the lens formula

1/v - 1/(-20) = 1/30

v = -60 cm

The final image is virtual and at a distance of 60 - 40 = 20 cm from the plane mirror.

Therefore, the final image would be formed at a distance of 20 cm from the plane mirror; it would be a virtual image.

Summary:

A point object is placed at a distance of 60 cm from a convex lens of a focal length of 30 cm. If a plane mirror were put perpendicular to the principal axis of the lens and at a distance of 40cm from it, the final image would be formed at a distance of -

A point object is placed at a distance of 60 cm from a convex lens of a focal length of 30 cm. If a plane mirror were put perpendicular to the principal axis of the lens and at a distance of 40cm from it, the final image would be formed at a distance of 20 cm from the plane mirror; it would be a virtual image.

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