What is electromagnwetic wave

Whatr is electromagnetic wave

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Hi John
What a question. This is a subject all on its own. I think far too complex for this forum. Although there may be simple ways to explain it they probably will never be complete and leave one with more questions.

Google “electromagnetic wave” and you will get lots of results. The Wikipedia entry looks pretty complete and is quite a large entry. I only had a quick look at it and it is quite complex but you will see what I mean when I said it is a study in itself.

I am afraid I am one of those who knows just enough to be dangerous. That is I have a good idea of what it is and does and its uses but leave all the nitty gritty details to the experts and just believe them. There are people who do nothing else but study this sort of thing.
Cheers Bob


Further to what @Robert93820 said, here are some examples of electromagnetic waves/radiation (they are the same thing, but radiation is a bit of a loaded term), starting at low frequency going up to high:

there’s also a lot of good information here :Anatomy of an Electromagnetic Wave | Science Mission Directorate

Essentially the “wave” is a combination of an electric field and a magnetic field, as the electric field decreases in strength the magnetic field increases, then it swaps. To make matters more confusing it’s a wave, but it’s also a particle: a photon. The wave view of it is useful when looking at the frequency.

There’s a lot of fear mongering around them and a lot of bogus products: e.g. peopleare scared about the emf radiation from wifi so people sell products to block it, however if the products worked, then the wifi wouldn’t, so you’d be better off just turning off the wifi router. The same with the stickers people put on their phones to block the ratiation, if the stickers worked, the phone wouldn’t.

Anyway… they are everywhere, we use them to see (light) transmit data (radio, wifi, mobile phones…) heat things (microwave), in medicine (x-rays, gamma-rays). I’m not sure if I’ve helped.


Well said, Doug. Generally, wave theory is the introduction to electromagnetic properties of light. The wave theory could not explain the quantum effects. It all started with the photoelectric effect. A concise explanation is in Wiki.

:slight_smile: Good concept, Robert. Just like water and fire. Know its power and treat with respect.


The way I think about it is “any time an electrically charged particle moves, it creates a magnetic wave. Any time a magnetic wave reaches an electrically charged particle, it moves the particle”. The analogy is throwing a stick into a pond. As it hits the water, ripples spread out. Another stick floating nearby will be affected by the passing wave. There are other similarities: the waves are travelling away from a center, but the nearby stick bobs up and down (at right angles to the passing wave). This is true of electrical movement and magnetic fields, they are at right angles to each other. Also, if the floating stick is lying horizontally on the water, the waves lift it quite effectively. But if the stick is standing vertical the waves pass by without affecting the stick as much. This is because the waves are polarized, the water moves up and down but not side to side. A lightning bolt is like the thrown stick, but most electrical signals are not, they are more like a paddle moving up and down creating a continuous series of waves. If this is done really fast, the distance between ripples is short. If it is done slowly then the ripples are far apart. For electromagnetic waves the formula is wavelength in kilometers is approximately 300,000/waves per second. Waves per second is measured in Hertz (abbreviation Hz). A typical FM station has a frequency somewhere between 88MHz (mega or million Hz) and 108MHz. So the wavelength is around 3 meters. Think about the floating stick again - if it were a heavy stick and the paddle was moved really quickly, the stick would not move much. But a light stick could bob up and down a lot more. So different “receivers” are affected differently by different wavelengths. There is no known limits to electromagnetic wavelengths, can vary from many kilometers to less than the width of an atom. Remembering that every charged particle is affected in some way, the size of that effect changes due to the electrical “weight” of the receiver. Every atom has electrical particles, the ones of interest are electrons. With the ‘right’ wavelength groups of electrons cooperate to produce a measurable effect. This happens inside a transformer, a radio receiver, the back of your eye, and many other circumstances. There is also no known limit to how far the waves travel. Telescopes receive light from unimaginable distances. And wiggling a few electrons in a probe outside the solar system (Voyager 1 at 14 billion kilometers) can induce a wiggle in a few cooperating electrons on earth, conveying messages.
I don’t know if that makes anything clearer. There are a lot of subtleties not mentioned, but starting with the ripples and the sticks and paddles works for me.


Electromagnetic waves or EM waves are waves that are created as a result of vibrations between an electric field and a magnetic field. In other words, EM waves are composed of oscillating magnetic and electric fields.