💯 Definition of the REFRACTIVE INDEX Explained with Clear Examples. Watch this Video to Find out! #2
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Question 1
The refractive index of moissanite is twice that of water. When light passes from water into moissanite, how does its speed change?
(A) Its speed doubles.
(B) Its speed quadruples.
(C) Its speed is halved. ←
(D) Its speed is quartered.
The relevant equation is Snell’s law: v1 / v2 = n2 / n1
Question 2
Which substance would you expect to have the highest refractive index?
(A) Hydrogen gas
(B) Helium gas
(C) Sapphire ←
(D) Sugar dissolved in water
Sapphire is the only solid, and the particles in a solid are more densely-packed than those of a liquid or gas.
Question 3
Given that in a vacuum (refractive index 1) light travels at c = 3.00 x 10^8 m/s, calculate the speed of light inside:
(a) a flask of glycerol, with a refractive index 1.47.
v2 = n1 x v1 / n2 = 1 / 1.147 x 3.00 x 10^8 = 2.04 x 10^8 m/s
(b) a ruby gemstone, with a refractive index 1.76.
v2 = n1 x v1 / n2 = 1 / 1.76 x 3.00 x 10^8 = 1.70 x 10^8 m/s
Question 4
When incoming light with an angle of incidence of 45 degrees shines from the air onto a topaz gem, it refracts at an angle of 26 degrees to the normal. Find its refractive index.
sin I / sin r = n2 / n1
n2 = sin 1 / sin r x n1 = sin 45 degrees / sin 26 degrees = 1.61
Question 5
If light passes through two materials with similar refractive indices, almost all light will be transmitted into the second material. With this in mind, explain why shards of broken glass are especially dangerous in the water.
Water and glass have similar refractive indices (1.3 and 1.5), so much of the light passing from one into the other is transmitted and not reflected.
This makes it very difficult to see the boundary between the glass and the water, so the shard of glass is almost invisible.