Question
Define Snell's law of refraction. A ray of light is incident on a glass slab at an angle of incidence of 60°. If the angle of refraction be 32.7°, calculate the refractive index of glass. (Given : sin 60° = 0.866, and sin 32.7° = 0.540).
Solution
According to Snell's law, the ratio of sines of the angles of incidence and refraction is constant for a given pair of mediums.
We get:
sin i /sin r = n (constant)
This constant is called refractive index.
According to the question:
Angle of incidence, i = 60°
Angle of refraction, r = 32.7°
Refractive index, n = ?
Applying the above formula, we get:
sin i / sin r = n
or, n = sin 60°/ sin 32.7°
= 0.866/0.540 = 1.60
Thus, the refractive index of glass is 1.60.
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You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in Table.
Material medium |
Refractive index | Material medium | Refractive
index |
Air | 1.0003 | Canada Balsam | 1.53 |
Ice | 1.31 | – | – |
Water | 1.33 | Rock salt | 1.54 |
Alcohol | 1.36 | – | – |
Kerosene | 1.44 | Carbon disulphide | 1.63 |
Fused quartz |
1.46 | Dense flint glass |
1.65 |
Turpentine oil | 1.47 | Ruby | 1.71 |
Benzene | 1.50 | Sapphire | 1.77 |
Crown glass |
1.52 | Diamond | 2.42 |