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).
(a) xπR2n1/n2
(b) xπR2n2/n1
(c) 2πRn1/n2
(d) πR2x
