Question

An object of 3 cm in size is placed at s distance of 10 cm from a concave mirror of focal length 20 cm. At what distance from the mirror should a screen be placed to get the sharp image? Find the size and nature of the image.​

Answer 1

Answer:

Given : h1 = 3 cm, u = - 10 cm, f = - 20 cm

We know that

1/v + 1/u = 1/f

⇒ 1/v = 1/f – 1/u = 1/(-20) – 1/(-10)

= - (1/20) + 1/10 = (-1 + 2)/20 = 1/20

∴ v = 20 cm

The image is formed at a distance of 20 cm behind the mirror.

And

m = - (v/u) = h2/h1

⇒ - (20)/(-10) = h2/3

⇒ h2 = 6 cm

Image is 6 cm in size, virtual and erect.