Question

An object is placed at a distance of 30cm infront of a concave mirror whose focal length is 15cm then the image distance is

Answer 1

Given ;

u = -30 cm
f = -15 cm
v = ?

Using mirror formula ;

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

(1/-15) = (1/v) + (1/-30)

1/v = (1/30) - (1/15)

1/v = (1-2)/30

v = -30 cm
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The image of formed at a distance of 30 cm in front of the concave mirror.
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Answer 2

Given,

Object distance, u = - 30cm

Focal length, f = - 15cm

Let's think the image distance is V

Now,

According to mirror formula,

1/f = 1/v + 1/u

or,1/- 15 = 1/v - 1/30

or, (-1/v) = (-1/30) + 1/15

or, 1/v = 1/30 - 1/15

or, 1/v = 1-2/30

or, 1/v = - 1/30

or,v = -30

So the object distance is -30cm in front of the mirror.

Hope it helps.