# Absorption/Emission of photons of specific frequency (Doppler Effect)

• feynomite
In summary, electrons in different energy states can absorb and emit photons of specific frequencies, but due to the Doppler Effect and the energy-time uncertainty principle, there is a margin of error in the frequency that a specific electron can absorb. This allows for the absorption of photons even when there is relative motion between the electron and the photon emission source. However, there is a limit to this margin of error due to the energy-time uncertainty principle.
feynomite
I recall being taught that electrons in various "orbitals" or "energy states" absorb and emit photons of a specific frequency. I also learned that relative speed changes the observed wavelength of photons, due to the Doppler Effect.

So, how is it that some electron can "absorb" a photon of a specific frequency if there is always going to be some movement relative to the electron and from where the photon was emitted? What is the "margin of error" in the frequency of a photon that a specific electron wil still absorb it?

In other words, assume that some bound electron in atom A1 moves from state S to S' and emits a photon of wavelength X. There's another electron A2 in state S' which absorbs X and switches to state S. I don't see how this can happen. I'm saying that A2 and A1 will nearly always have some motion relative to each other, and thus X leaving A1 is different from X arriving at A2 (unless there is some margin of error where the electron can absorb frequencies in the range Y to Z, and X is within this range).

Could anyone provide insight into this? I must be misunderstanding something.

feynomite said:
I recall being taught that electrons in various "orbitals" or "energy states" absorb and emit photons of a specific frequency. I also learned that relative speed changes the observed wavelength of photons, due to the Doppler Effect.

So, how is it that some electron can "absorb" a photon of a specific frequency if there is always going to be some movement relative to the electron and from where the photon was emitted? What is the "margin of error" in the frequency of a photon that a specific electron wil still absorb it?

In other words, assume that some bound electron in atom A1 moves from state S to S' and emits a photon of wavelength X. There's another electron A2 in state S' which absorbs X and switches to state S. I don't see how this can happen. I'm saying that A2 and A1 will nearly always have some motion relative to each other, and thus X leaving A1 is different from X arriving at A2 (unless there is some margin of error where the electron can absorb frequencies in the range Y to Z, and X is within this range).

Could anyone provide insight into this? I must be misunderstanding something.

No, when A1 leave new state the A2 not SAME. It different, must be that when absorbs.

I'm hoping someone will be able to shed some light on this question... it's pretty straightforward and I'm sure someone has the answer.

Thanks

Atomic transitions have a natural "linewidth" because of the energy-time uncertanity principle, so there is actually a small range of allowable energies.

## 1. What is the Doppler Effect?

The Doppler Effect is the 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 sound waves, light waves, and other types of waves.

## 2. How does the Doppler Effect affect the absorption and emission of photons of specific frequency?

The Doppler Effect causes a shift in the frequency of light waves emitted or absorbed by a moving source. This means that the frequency of the photons will appear higher or lower depending on the relative motion between the source and the observer. This effect is important in understanding the movement of stars and galaxies and is also used in technologies such as Doppler radar.

## 3. What determines the amount of frequency shift in the Doppler Effect?

The amount of frequency shift in the Doppler Effect is determined by the relative velocities of the source and the observer. If the source is moving towards the observer, the frequency will appear higher (blue shift), and if the source is moving away from the observer, the frequency will appear lower (red shift). The amount of shift also depends on the speed of the source and the wavelength of the wave.

## 4. How does the Doppler Effect influence our understanding of the universe?

The Doppler Effect is crucial in helping scientists understand the behavior and movement of objects in the universe. By analyzing the red and blue shifts in the light from stars and galaxies, we can determine their relative motion and understand how they are moving and interacting with each other. This information has led to significant discoveries and advances in our understanding of the universe.

## 5. Can the Doppler Effect be observed in other types of waves besides light and sound?

Yes, the Doppler Effect can be observed in other types of waves such as water waves, seismic waves, and even radio waves. In fact, the principles of the Doppler Effect can be applied to any type of wave that exhibits a change in frequency due to relative motion between the source and the observer.

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