# A monochromatic light passes through a glass slab (μ = 1.5) of thickness 9cm in time t1. If it takes a time t2 to travel…..

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

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