What exactly is the definition of an EM wave?

[k9b4]

Do we say something is an EM wave only if the EM field is oscillating at a constant frequency? What exactly is the definition of an EM wave?

If an electron moves in a direction and then stops moving, is an EM wave produced by that electron?

 

[ShayanJ]

An EM wave is a change in the EM field propagating in space. Its a signal that tells different parts of the space to update their value of the field. Any acceleration present in the charge distribution causes an EM wave. Changing magnetic fields may cause EM waves too.

 

[Nugatory]

Do we say something is an EM wave only if the EM field is oscillating at a constant frequency?

No. The wave equation is linear, so any two of its solutions can be added to yield a third. Electrical and magnetic fields also add, so if I have two oscillators at different frequencies, the resulting electrical and magnetic field will also be a solution to the wave equation. It won't be a neat pure sine wave with a definite frequency, and by adding enough different frequencies and amplitudes you can produce almost arbitrarily complicated waveforms.

What exactly is the definition of an EM wave?

I don't know that there's a single exact definition, but I'd expect just about everyone to agree that any time-varying electromagnetic field that can be written as a sum of terms containing ##e^{i(kx-vt)}## would be one.

If an electron moves in a direction and then stops moving, is an EM wave produced by that electron?

Yes. It will be a single pulse, but it will be a wave.

 

[sophiecentaur]

People often confuse the term "wave" with a "Carrier wave", which is a single frequency (sin wave) and of long duration.

 

[sardar]

An EM wave, or electromagnetic wave, is a type of energy that is created by the movement of electrically charged particles, such as electrons. It is a form of energy that travels through space in the form of oscillating electric and magnetic fields. This means that as the wave moves, the electric and magnetic fields are constantly changing and interacting with each other.

The frequency of an EM wave refers to the number of oscillations per second, and it is one of the defining characteristics of an EM wave. However, an EM wave can also have a range of frequencies, not just a constant one. For example, visible light is a type of EM wave and it has a range of frequencies within the electromagnetic spectrum.

So, to answer the question, we can say that an EM wave is defined as a type of energy that is created by the movement of electrically charged particles and has oscillating electric and magnetic fields. The frequency of the wave can vary, but it is a characteristic of an EM wave.

In regards to the second question, if an electron moves in a direction and then stops moving, it may produce a brief EM wave, but it would not be a sustained wave with a constant frequency. Therefore, it would not fit the definition of an EM wave.