Question

Q. An object is placed before a concave lens of focal
length 12 cm. The size of the image formed by the
lens is half the size of the object. Calculate the
distance of the object from the lens.
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Answer 1

Answer:

12 cm

Explanation:

f = -12 cm ( It is a concave lens)

Let image distance be v cm and object distance be u cm.

Since,

1/f = 1/v - 1/u ----1

and

m = v/u

i.e m = 1x/2/x (x is the height of object)

m = 1/2

Thus,

1/2 = v/u

v = u/2. ----2

using 2 in 1:-

1/f = (1/u/2) - 1/u

1/f = 2/u -1/u

1/f = 1/u

u = f

u = -12 cm

Thus object distance is 12 cm.