Question

A spherical mirror forms a real image of a point object placed infront of it. The

distances of the image and the object from the mirror are 30cm and 0.2m respectively

then the focal length and nature of the mirror are

1. 120 mm, Concave 2. 120mm, Convex 3.60 cm, concave 4. 60cm, Convex​

Answer 1

Answer: Focal length = -12cm (-120mm), Concave mirror. Negative focal length because it is a concave mirror.

Explanation

u = -0.2m = -20cm,  v = -30cm,   f = ?

Use mirror formula

1/v + 1/u = 1/f

1/-30 + 1/-20 = 1/f

    1/-12          =   1/f

    -12cm       =   f

therefore, focal length is -12cm = -120mm

Negative focal length indicates it is a Concave mirror.

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