What is the trough in destructive interference of EM?

In summary, the crest and trough of an electromagnetic wave refer to the maximum and minimum values of the electric/magnetic field in opposite directions. The energy of the wave is not located at the crest, but is proportional to the magnitude of the electric field. This can be calculated by integrating the intensity over the transverse area and with time. The crest is not a photon, and there is no negative or anti-photon at the trough.
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student34
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My textbook says that the trough of the electromagnetic wave cancels out when it meets a crest. Okay, that makes sense, but if the crest is the actual photon/wave of energy, what is this trough that can cancel out the energy? It seems to mean that there are "negative energy photons" in between each "normal" photon.
 
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The crest in the electric/magnetic field is the electric/magnetic field vector with the largest magnitude, it's not the energy. The energy in an electromagnetic wave is proportional to the quantity
$$
\int \int |\mathbf{E}(\mathbf{r}_\perp,t)|^2 d\mathbf{r}_\perp dt
$$.
where ##\mathbf{r}_\perp## are coordinates in the transverse plane.
 
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  • #3
blue_leaf77 said:
The crest in the electric/magnetic field is the electric/magnetic field vector with the largest magnitude, it's not the energy. The energy in an electromagnetic wave is proportional to the quantity
$$
\int \int |\mathbf{E}(\mathbf{r}_\perp,t)|^2 d\mathbf{r}_\perp dt
$$.
where ##\mathbf{r}_\perp## are coordinates in the transverse plane.
I don't know the mathematical explanations of this, so I am wondering if you would you say that the crest is the photon? If so, the trough seems to being negating the photon for the moment that they meet. Is this right?
 
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student34 said:
I don't know the mathematical explanations of this, so I am wondering if you would you say that the crest is the photon? If so, the trough seems to being negating the photon for the moment that they meet. Is this right?

No, the crest is not a photon. Be careful mixing classical and quantum physics like that. The crest is the maximum value of the E field in one direction and the trough is the maximum in the exact opposite (or minimum in the first). There is not a photon at the crest and an negative or anit- photon at the trough.
 
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student34 said:
I don't know the mathematical explanations of this, so I am wondering if you would you say that the crest is the photon? If so, the trough seems to being negating the photon for the moment that they meet. Is this right?
It follows from the definition of intensity as the energy density passing through a transverse plane per unit area per unit time. Intensity is proportional to the magnitude squared of electric field. If you want to get the energy, you then need to do the inverse operation as that to obtain the intensity, namely integrate intensity over the transverse area and then integrate with time.
 

Related to What is the trough in destructive interference of EM?

1. What is the trough in destructive interference of EM?

The trough in destructive interference of electromagnetic (EM) waves refers to the point of minimum amplitude in the combined wave resulting from the superposition of two or more waves with opposite phases.

2. How is the trough formed in destructive interference of EM?

The trough is formed when two or more EM waves with the same frequency and amplitude overlap and their peaks and valleys line up in opposite directions, causing them to cancel each other out.

3. What is the significance of the trough in destructive interference of EM?

The trough represents the point of complete cancellation of EM waves, resulting in zero amplitude and no energy being transferred at that point. This is important in applications such as noise cancellation and creating standing waves.

4. How does the distance between the sources of EM waves affect the position of the trough?

The distance between the sources of EM waves affects the position of the trough by changing the phase relationship between the waves. As the distance increases, the phase shift between the waves also increases, resulting in a shift in the position of the trough.

5. Can the trough in destructive interference of EM be manipulated?

Yes, the position and amplitude of the trough can be manipulated by changing the frequency, amplitude, and phase of the EM waves. This is commonly done in applications such as signal processing, noise cancellation, and creating interference patterns.

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