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Question

# An object of length 4 cm is placed in front of a concave mirror at a distance of 30 cm. The focal length of mirror is 15 cm. Where will the image form?

A
15 cm behind the mirror.
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B
15 cm in front of mirror.
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C
30 cm behind the mirror.
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D
30 cm in front of mirror.
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Solution

## The correct option is D 30 cm in front of mirror.The relationship between the radius of curvature and focal length is that the radius of curvature is twice the focal length.In this case, focal length of the concave mirror is given as 15 cm. Hence, the radius of curvature is 15×2=30cm.A point in front of a concave mirror, on its principal axis, such that parallel rays travelling parallel to the principal axis, after reflection actually converge at this point. When the image forms on the object, then the object as well as the image are situated at centre of curvature of concave mirror.The distance between the object and mirror is given as 30 cm.Hence, the image will also form at a distance of 30 cm in front of the mirror as the radius of curvature and the object distance are the same.

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