Does doppler effect affect ENERGY of photon?

In summary, the Doppler effect affects the energy of a photon and can cause the frequency of photons reaching an observer to decrease. The human eye perceives color based on the frequency (or energy) of a photon in the observer's reference frame. The energy and frequency of a photon are frame-dependent and there is no such thing as an intrinsic frequency of a photon. Therefore, the energy and frequency of a photon can change based on the observer's velocity. This applies to experiments measuring photoelectric effect as well.
  • #1
ARAVIND113122
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does doppler effect affect ENERGY of photon??

i have tried to make the question as clear as possible,but in the process,have made it a bit too long. i request you to be patient-
suppose a source is emitting a photon after equal intervals of time.an observer,who was initially at rest w.r.t the source,starts to move away from it.this would increase the time interval after which the photon reaches the observer.this means that the frequency of photons reaching the observer decreases,i.e,the apparent wavelength of light increases.

now,energy of a photon is given by e=h√.
suppose the photons emitted by the source have frequency corresponding to that of blue light.when the observer starts to move away,the light,according to the observer,would seem to have shifted towards the red end of the spectrum .

am i right in saying that although the actual frequency of each individual photon[which gives it its energy] remains the same,the frequency PERCEIVED by the human eye decreases?to be more specific,i want to know if the human eye perceives colour based on the INTRINSIC frequency of a photon,or the frequency with which successive photons hit the eye.
if the latter is true,then it wouldn't it mean that an EM wave of ANY frequency can be perceived as that of ANY OTHER frequency by the eye[despite having different energies according to their ACTUAL frequencies{given by E=h√}],depending on the motion of the source w.r.t the source?
or does doppler effect affect the initial frequency of the photon?if so,how?
is the answer a combination of different factors?if yes,how?
 
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  • #2


Both the energy and frequency of a photon depend on the observer's reference frame. There is no such thing as "actual" (absolute) frequency or energy, for a photon.

When a photon enters your eye, the sensation of color that it produces depends on its frequency (or energy) in your reference frame.

Indeed, in principle if you accelerate to a high-enough velocity towards an oncoming photon, you can change it (from your point of view) from a green photon to an ultraviolet photon, and even further, to an X-ray or gamma-ray photon.
 
  • #3


ARAVIND113122 said:
i have tried to make the question as clear as possible,but in the process,have made it a bit too long. i request you to be patient-
suppose a source is emitting a photon after equal intervals of time.an observer,who was initially at rest w.r.t the source,starts to move away from it.this would increase the time interval after which the photon reaches the observer.this means that the frequency of photons reaching the observer decreases,i.e,the apparent wavelength of light increases.

now,energy of a photon is given by e=h√.
suppose the photons emitted by the source have frequency corresponding to that of blue light.when the observer starts to move away,the light,according to the observer,would seem to have shifted towards the red end of the spectrum .

am i right in saying that although the actual frequency of each individual photon[which gives it its energy] remains the same,the frequency PERCEIVED by the human eye decreases?to be more specific,i want to know if the human eye perceives colour based on the INTRINSIC frequency of a photon,or the frequency with which successive photons hit the eye.

There is no such thing as the INTRINSIC frequency of a photon. The energy of the photon is frame dependent. The energy of a photon and thus its frequency as measured by someone at rest with respect to the source will be different than that it would be for some one moving with respect to the source. Put another way, there is no measurable difference between a "red" photon emit by a source at rest with respect to you and a "red" photon that has undergone Doppler shift.
 
  • #4


okay.consider a case when someone is conducting an experiment to measure current produced by photo-electric effect.the threshold frequency is that of "blue" photons.but the source is emitting "green" photons.then,is it true that if he moves the object at a minimum required speed towards the source,he would observe photoelectric effect??
 
  • #5


ARAVIND113122 said:
okay.consider a case when someone is conducting an experiment to measure current produced by photo-electric effect.the threshold frequency is that of "blue" photons.but the source is emitting "green" photons.then,is it true that if he moves the object at a minimum required speed towards the source,he would observe photoelectric effect??

Absolutely. The Cosmic Microwave Background itself becomes lethal x-ray/gamma radiation if you accelerate to a high enough velocity.
 
  • #6


There's nothing magical about photons. The energy of a photon depends on the observer's velocity. The energy of an automobile depends on the observer's velocity.
 
  • #7


Thank you very much!
 

1. What is the Doppler effect?

The Doppler effect is a phenomenon where the frequency of a wave appears to change when the source of the wave is in motion relative to the observer. This can be observed in various waves such as sound, light, and water waves.

2. Can the Doppler effect affect the energy of a photon?

Yes, the Doppler effect can affect the energy of a photon. When a photon moves towards or away from an observer, the frequency of the wave changes due to the Doppler effect. As a result, the energy of the photon also changes, following the equation E=hf, where h is Planck's constant and f is the frequency of the photon.

3. How does the Doppler effect affect the energy of a photon?

The Doppler effect affects the energy of a photon by changing its frequency. When a photon moves towards an observer, its frequency increases, and its energy also increases. Conversely, when a photon moves away from an observer, its frequency decreases, and its energy also decreases.

4. Is the energy of a photon affected by the Doppler effect in all directions?

No, the energy of a photon is only affected by the Doppler effect in the direction of motion. If a photon is moving at an angle to the observer, the Doppler effect will only affect its energy in the component of motion towards or away from the observer.

5. Can the Doppler effect change the type of energy of a photon?

No, the Doppler effect does not change the type of energy of a photon. The energy of a photon is determined by its frequency, and the Doppler effect only affects the frequency of a photon, not its type of energy. For example, a photon of visible light will still have the same type of energy (electromagnetic energy) even if its frequency changes due to the Doppler effect.

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