High School Quantisation of light and Doppler effect

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Light is quantized into photons, and the Doppler effect for light can be explained through the frame-dependent nature of photon frequency and energy. The frequency of a photon changes based on the relative motion of the source and observer, which does not violate conservation of energy, as energy is also frame-dependent. An analogy is made with kinetic energy, where an object's energy varies depending on the observer's frame of reference. The discussion emphasizes that while energy can change with motion, it remains conserved within the appropriate frame. Understanding the Doppler effect in light requires acknowledging these principles of relativity and energy conservation.
Vibin Narayanan
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Light consists of quanta(small packets of energy). Then how do we explain doppler effect of light the same way we do for sound? What is the valid explanation of light doppler effect which is consistent with the photon picture?
 
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Vibin Narayanan said:
Light consists of quanta(small packets of energy). Then how do we explain doppler effect of light the same way we do for sound? What is the valid explanation of light doppler effect which is consistent with the photon picture?
The frequency of the photon (and hence its energy) is frame-dependent.
 
DrClaude said:
The frequency of the photon (and hence its energy) is frame-dependent.
That's it? I simply didn't get it. Energy changing with the motion of source or observer or both, doesn't violate conservation of energy?
 
Energy is conserved, but it is dependent on the frame. For example, I will measure a ball moving relative to me as having kinetic energy, but in a frame co-moving with the ball, it will have none.
 
Vibin Narayanan said:
That's it? I simply didn't get it. Energy changing with the motion of source or observer or both, doesn't violate conservation of energy?

Nope. Consider yourself in a car moving down the road. If another car comes up behind you 1 mph faster than you're going and taps your bumper, your car is not totaled, despite the fact that you both may be traveling 70+ mph.
 

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