Q. A monochromatic light passes through a glass slab (μ = 1.5) of thickness 9 cm in time t1. If it takes a time t2 to travel the same distance through water (μ = 4/3). The value of (t1 − t2) is
(a) 5 × 10-11 sec
(b) 5 × 10-8 sec
(c) 2.5 × 10-10 sec
(d) 5 × 10-10 sec
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Ans: (a)
Sol: Distance d= 9 × 10−2 m , Speed in medium v= c/μ and
time t= distance/ speed
$ \displaystyle t_1 = \frac{9 \times 10^{-2}}{c/1.5} $
$ \displaystyle t_2 = \frac{9 \times 10^{-2}}{c/(4/3)} $
t1 – t2 = 5 x 10-11 sec