Question

A spherical mirror has a focal length of 20cm. When an object is placed at a certain distance from the mirror, the mirror produces the magnification of + 4/3. Find the position of the image.

Answer 1

Answer:

Given :

focal length, f = 20 cm

magnification , m = -v=4

u 3

v = -4x

u = 3x

formulae : 1/f = 1/v + 1/u

1/20 = 1/-4x + 1/3x

1/20 = -3 + 4

12x

1/20 = 1/12x

x = 1.6

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image distance , v = -4.8 cm

it is a Convex mirror

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Answer 2

Explanation:

here,

magnification = +4/3 = h'/h

height of image is more than height of object and image is virtual erect (m is +ve).

therefore the given mirror is concave.

Hence, f = -20 cm.

Now,

let image distance = v

object distance = u

by magnification, -v/u = 4/3

v = - 4u/3

1/f = 1/v + 1/u

-3/4u + 1/u

-3 + 4 / 4u

1/-20 = 1/4u

u = - 5 cm.

now v = -4u/3

20/3 cm

therefore position of image = 20/3 cm.