Question

If the magnification produced by converging lens is 2 and the object distance is 20cm then find the focal length of the lens.

Answer 1

Answer:

Object distance, -u =20cm

magnification, m = 2

m= v

-----

u

so, 2= v

-----

- 20

2 ×-20 =v

v=-40

1/v +1/u =1/f

so, 1/-40 + 1/-20=1/f

-1/40 -1/20=1/ f

-1+(-2) /40=1/ f

-3/40=1/ f

so, f = -40/3

f = -13. 33 cm

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