Question

A virtual image is formed by a concave mirror of focal length of 20 cm. The size of the image is double the size of the object.(i) the object distance (ii) the image distance.
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Answer 1

Explanation:

since it's a virtual image, in. a concave mirror

the image is between pole and focus

and focal length is 20 cm

so distance of image is <20cm

u of image is 2 x of u

I e.

in mirror formula

1/v + 1/u = 1/f

i.e. 1/-2u - 1/u = 1/-20

u=-30

and again keeping it in mirror formual

1/v+ 1/u = 1/f

1/v - 1/30 = -1/20

=> v = 10

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Answer 2

Answer:

Object distance = - 10 cm

Image distance = 40 cm

Explanation: Given:- f = -20 cm , hi = 2ho , u = ? and v = ?

According to the question:-

According to the magnification formula :-

m = hi/ho = - v/u

2ho/ho = - v/u

2 = - v/u

2u = - v

v = - 2u ........(1)

According to the mirror formula:-

1/u + 1/v = 1/f

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

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

1 / 2u = - 1/20

u = - 10 cm

Putting value of u = - 10 in equation

v = - 2u

v = - 2 × - 10

v = 40 cm

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