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1. A lens has a refractive index 1.5 and itsfocal length is 20 cm while in air. The samelens is put in a liquid having 1.25 refrac-tive index. So find the focal length of thelens while in liquid.

Answer»

20.20 is the correct answer

sorry it is wrong

ok

we can use the lens makers formula to solve this problem. Lens makers formula is

For lens in air

1/20 = (1.5–1)(1/R1–1R2) (1/R1 - 1/R2) = 2/20 = 1/10

When lens immersed in water1/f'= (1.5/1.25 –1)(1/R1–1/R2)

1/f' = (6/5 - 1) * 1/10

1/f' = (1/5) * 1/10

f' = 50 cm



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