Question

3. A flat sheet of ice has a thickness of 1.7 cm. It is on top of a flat sheet of crown glass that has a thickness of 1.1 cm. Light strikes the ice perpendicularly and travels through it and then through the crown glass. In the time it takes the light to travel through the two sheets, how far would it have traveled in a vacuum?

Answer 1

Let d1 = 1.7 cm = 0.017 m
we know refractive index of Ice, n1 = 1.309
let d2 = 1.1 cm = 0.011 m
refractive index of crown glass, n2 = 1.517

speed of light in Ice, v1 = c/n1 = 3*10^8/(1.309) = 2.292*10^8 m/s
speed of light in crown glass, v2 = c/n2 = 3*10^8/(1.517) = 1.978*10^8 m/s

total time taken, t = t1 + t2

= d1/v1 + d2/v2

= 0.017/(2.292*10^8) + 0.011/(1.978*10^8)

= 1.2978*10^-10 s

The distance would have travelled by the light in this time,

L = c*t

= 3*10^8*1.2978*10^-10

= 0.039 m

= 3.9 cm <<<<<<-----Answer