A lens of focal length 15 cm is dippend in water

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A lens of focal length 15 cm is dipped in water. What is the new focal length given that ref index of glass wrt air is 3/2 and that of water wrt air is 4/3.
If the lens is dipped in a liquid under what condition, the rays
are not deviated.

#Physics #Optics

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5 Answers

Gaurav ·2010-02-11 05:22:48

Re:

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Manmay kumar Mohanty ·2010-02-11 05:36:22

Is the ans. 58.59 cm.

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Gaurav ·2010-02-11 08:26:45

i don't know the answer yaar.. please tell how u calculated??

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soumyadeep sanyal ·2010-02-11 09:07:32

the ans is 60 cm.
ref index of glass wrt water is (3/2)/(4/3)=9/8
now use lens makers formula...r1,r2 being the same in both cases would cancel.
f2/f1=(Î¼1-1)/(Î¼2-1)
f2=focal length in water.
Î¼1=3/2
Î¼2=9/8
f1=15

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Manmay kumar Mohanty ·2010-02-14 05:41:20

1f₁ = (32 - 1) [1R₁ - 1R₂] .........(1)

1f₂ = (3/24/3 - 1) [1R₁ - 1R₂] .........(2)

Dividing (1) by (2),
f₂f₁ = 0.50.128

f₂ = 0.5 x 150.128

f₂ = 7.50.128 = 58.59 cm.
Is it correct.

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A lens of focal length 15 cm is dippend in water

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