Question

An object is placed at a distance of 30 cm from a convex mirror, the magnification produced is 1/2 Where should the object be placed to get a magnification of 1/3...?
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Answer 1

Answer:

The object should be placed at a distance of 20cm.

Explanation:

In first case when magnification is 1/2

v/u = 1/2

  v = u/2  

   = 30/2

   = 15

From mirror formula ,

1/v + 1/u = 1/f

1/30 + 1/15 = 1/f

f = 10cm

Thus focal length =10cm

In second case.

v/u = 1/3

   u = 3v

From mirrors formula,

1/u + 1/v = 1/f

1/3v+1/v=1/10

2/3v=1/10

3v = 20

v = 20/3cm

Since, u= 3v

Therefore, u = 3 x 20/3

                   u = 20cm

Answer 2

Answer:

Hence, the object should be placed at a distance of 60cm in front of a convex to get the magnification of 1/3.