Question

An object is 8 cm high. It is desired to form a real image 4 cm high at 60 cm from the mirror. The type of mirror needed with the focal length is -- (a) convex mirror with focal length f=40 cm (b)convex mirror with focal length f=20 cm (c) concave mirror with focal length f=-40 cm (d)concave mirror with focal length f=-20 cm Any wrong answers or spam will be reported. Please answer with steps.

Answer 1

Answer:

Option(A)

Explanation:

Given,

Height of object(h₀) = 8 cm

Focal length of convex mirror = ?

Object distance u = ? cm

Image distance v = 60 cm

Image height(hi) = 4 cm

Magnification m = hi/ho = 4/8 = 1/2

So,

=> v/u = 1/2

=> 60/u = 1/2

=> u = 120 cm

Now,

Mirror Formula :

(1/v) + (1/u) = 1/f

=> (1/60) + (1/120) = 1/f

=> 1/40 = 1/f

=> f = 40 cm

Therefore,

Type of mirror needed with focal length is :

Convex mirror with focal length f=40 cm

Hope it helps!