aamc 9, #47

[riseNshine]

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47) Visible light travels more slowly through an optically dense medium than through a vacuum. A possible explanation for this could be that the light:

A) is absorbed and re-emitted by the atomic structure of the optically dense medium
B) is absorbed and re-emitted by the nucleus of the material in the optically dense medium
C) bounces around randomly inside of the optically dense medium before merging
D) loses amplitude as it passes through the optically dense medium

Answer saysA..but if it's absorbed and re-emitted, doesn't that mean it loses some energy when it drops back down so it's of a higher wavelength and by v=wavelength*Frequency, the speed would be faster?

 

[LianaStan]

The universal speed limit is the speed of light, speed cannot be faster. By this logic, as wavelength increases, frequency decreases inversely when energy is lost. This is also given by E=hf. Edit: In a non-vacuum medium, the speed decreases as wavelength increases while frequency stays the same.

As for whether light loses energy as it is absorbed and re-emitted, in most scenarios, fluorescence will be of lesser energy (seen when some objects absorb UV light (invisible to us) but re-emits as visible light). The idea here is that there is a lag time between absorption and re-emission.