Discussion
A ray of light travels from air into three media A, B and C with different optical densities. Refer to the table given below and identify X, Y, Z and W :
| Change in speed of light | Change in frequency of light | Change in wavelength of light | |
|---|---|---|---|
| Air to medium A | X | Y | Decreases |
| Air to medium B | Increases | No change | Z |
| Air to medium C | Remains same | W | No change |
Choose the correct option.
Answer: C
The correct option is X - Decreases; Y - Remains unchanged; Z - Increases; W - Remains unchanged.
When light passes from one medium to another, its frequency never changes; it is set by the source. So Y and W are both 'remains unchanged'. Since speed = frequency × wavelength, the speed and the wavelength change together, in the same direction.
Into medium A the wavelength decreases, so the speed decreases too (X). Into medium B the speed increases, so the wavelength increases too (Z). Every option in which the frequency changes is therefore wrong, which leaves only X - Decreases; Y - Remains unchanged; Z - Increases; W - Remains unchanged.
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