Optics Question 135

Question: The apparent depth of water in cylindrical water tank of diameter 2R cm is reducing at the rate of x cm/minute when water is being drained out at a constant rate. The amount of water drained in c.c. per minute is (n1 = refractive index of air, n2 = refractive index of water)

[AIIMS 2005]

Options:

A) x p R2 n1/n2

B) x p R2 n2/n1

C) 2 p R n1/n2

D) p R2 x

Show Answer

Answer:

Correct Answer: B

Solution:

Apparent depth h=hairμliquid

Therefore dhdt=1aμw=1aμwdhdt

Therefore x=1aμwdhdt

Therefore dhdt=aμwx Now volume of water V=πR2h

Therefore dVdt

=πR2dhdt

=πR2.aμwx

=aμwπR2x

=μwμaπR2x

=(n2n1)πR2x



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