`` NEWTON: Light Beats
 
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Name: Kate
Status: other
Grade: 12+
Country: Australia
Date: Summer 2013


Question:
I am aware that two sound waves can overlap and result in a beat, and the frequency of the beat can be heard as a distinct third sound wave. Is the same possible for light? Can two light waves of different frequencies interfere and result in a third light wave being perceived?

Replies:
Yes, although it's hard to achieve the conditions in which this can be observed. The only example I've ever seen is the scattering of x rays by a Mossbauer nucleus. The incident light excites nuclear resonances (when I say "excites a nuclear resonance", you should think "rings a bell inside the nucleus") that have very slightly different frequencies, and the radiation from those resonances interferes, producing a beat frequency that is the difference between the frequencies of the resonances.

However, in most cases of visible light interfering with visible light, the difference frequency will be lower than the frequency of visible light, so you will not actually perceive a third light wave.

Tim Mooney


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