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For electromagnetic waves, how do the presence of electric and magnetic fields of an oscillating charge, say in the sun, exist and have an effect on entities, 150 million kilometers away, on Earth.

For example, a single charge, 150 million kilometers away from earth, in space. Its electric/magnetic field will not have any affect on anything on earth, correct me if I'm wrong, so how does the oscillation of it change this fact.

Bear in mind that I am a high school physics student, so please, if this is a stupid question, please tell me.

  • 1
    $\begingroup$ It is because static fields decrease with one over the square of the distance (like gravity) whereas dynamic/oscillating fields decrease with one over the distance. This makes a huge difference at large distances. (Right now I don't know how to explain why it is like that except that the equations give us this results...) $\endgroup$
    – EigenDavid
    Aug 25, 2017 at 11:29
  • $\begingroup$ have a look at this answer physics.stackexchange.com/questions/353602/… on how electromagnetic waves are created, and links therein $\endgroup$
    – anna v
    Aug 25, 2017 at 12:20

2 Answers 2


You must understand that electric and magnetic fields are not really independent of each other, but rather they are infact simply two different aspects of a single entity called an electromagnetic field. This field manifests itself in different forms based on choice of frame, and other factors.

Now, there are some interesting facts, about electric fields and magnetic fields. One very important fact is that changing electric fields produce a magnetic field, and that changing magnetic fields produce an electric field. These are the Ampère's and Faraday's laws respectively. I won't discuss too much about them here, but head to the Further Reading section of this answer if you'd like to dig deeper.

Anyway, in an electromagnetic wave, the electric field intensity is an oscillating value. This electric field that constantly changes, produces a magnetic field. The magnetic field, like the electric field, is also a sinusoidal function, which in turn, generates another electric field. This interconversions keep on going, and the wave propagates as a result. The energy of the wave remains constant, and simply transfers back and forth between the electric and magnetic manifestations of the electromagnetic wave. This energy can be carried at a very specific speed $c$ away from the source of the elecromagnetic wave and taken elsewhere. This is exactly how the Sun can transfer energy to the Earth.

Further reading:

  1. Ampère's Law
  2. Faraday's Law
  3. Electromagnetic Wave

I will start by saying that an electron many millions of kilometers away from earth does in fact have an effect on earth, but it is just a very small effect.

Anyway, the main thing that can increase the effect of the electron when it begins oscillating is that the oscillations can be as big as you can imagine. Suppose you have a single electron oscillating at the frequency of green light. If the amplitude of oscillation is very small, you wouldn't be able to see this electron from earth. But as the oscillation gets bigger, the oscillating electron will look brighter and brighter.

This is what allows the sun to be so bright. The sun is generating energy from fusion, and this energy must radiate away from the sun, and some amount of it does so in the form of light. The more fusion happens in the sun, the more the electrons vibrate, and the more electromagnetic radiation is emitted from the sun. It happens that the sun is generating enough power that it looks bright.


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