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Question
The following table gives the refractive indices of a few media:
| 1 | 2 | 3 | 4 | 5 | |
| Medium | Water | Crown glass | Rock salt | Ruby | Diamond |
| Refractive index | 1.33 | 1.52 | 1.54 | 1.71 | 2.42 |
Use this table to give an example of:
(i) a medium pair so that light speeds up when it goes from one of these medium to another.
(ii) a medium pair so that light slows down when it goes from one of these medium to another.
Solution
(1) Light speeds up as it travels from a denser medium to a rarer one, ie., from a medium with a higher refractive index to one with a lower refractive index. An example would be the medium pair of diamond and water, where light travels from diamond to water.
(2) Using the same argument, light slows down as it travels from a medium with a lower refractive index to one with a higher refractive index. Therefore, the medium pair of crown glass and ruby can be taken as an example, where light moves from the crown glass to the ruby.
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The velocity of light in a medium is 1.5 x 108 m/s. What is the refractive index of the medium with respect to air, if the velocity in air is 3 x 108 m/s?
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| 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 | – | – |
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| Fused quartz | 1.46 | Dense flint glass | 1.65 |
| Turpentine oil | 1.47 | Ruby | 1.71 |
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