Question

An object is placed in front of a concave mirror of a. focal length 20 cm to form a real image at a distance of 50 cm. find the object distance ​

Answer 1

Explanation:

Given that :

Focal length (f) = -20 cm

Image distance (v) = -50 cm

Asked :

Object distance (u) = ?

By using mirror formula,

1/f = 1/v + 1/u

1/-20 = 1/-50 + 1/u

1/u = 1/-20 - 1/-50

1/u = 1/-20 + 1/50

1/u = -5 + 2/ 100 (by doing LCM)

1/u = -3/100

1/u = -1/33.3

u = -33.3 cm (by reciprocal)

Therefore Object distance (u) = -33.3 cm

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