# Is my understanding of electromagnetic waves correct [closed]

My understanding of electromagnetic waves is that earths core has charged particles, so there is an electric field, when those charged particles move they will create a magnetic field and earth has a magnetic field. Electromagnetic waves are caused by electric and magnetic waves, so sense the earth supports both of these, electromagnetic waves can exist in the air, am I correct, if not please tell me how electromagneitc waves work. I have asked why don't electromagnetic waves need a vaccum to move through but the answer are to complicated , so if your going to answer please answer as if you were talking to your fiend who knows nothing about physics, please do not anwers as if you were talking to another physicist.

• Are you asking how the earth's magnetic field is generated? Electromagnetic waves are far more general, they don't need a planet like earth. Light is electromagnetic waves! It travels through vacuum but also through anything else (some things better than others). – Adomas Baliuka Feb 26 '17 at 3:14
• This site was invented to facilitate interaction between physicists and physics students with other physicists. You may get answers here, but you might get a better response at a more appropriate site. Here’s one to consider., but there are others. – garyp Feb 26 '17 at 3:38

My understanding of electromagnetic waves is that earths core has charged particles, so there is an electric field, when those charged particles move they will create a magnetic field and earth has a magnetic field.

Right at the heart of the Earth is a solid inner core, two thirds of the size of the Moon and composed primarily of iron. At a hellish 5,700°C, this iron is as hot as the Sun’s surface, but the crushing pressure caused by gravity prevents it from becoming liquid.

Surrounding this is the outer core, a 2,000 km thick layer of iron, nickel, and small quantities of other metals. Lower pressure than the inner core means the metal here is fluid.

Differences in temperature, pressure and composition within the outer core cause convection currents in the molten metal as cool, dense matter sinks whilst warm, less dense matter rises. The Coriolis force, resulting from the Earth’s spin, also causes swirling whirlpools.

This flow of liquid iron generates electric currents, which in turn produce magnetic fields. Charged metals passing through these fields go on to create electric currents of their own, and so the cycle continues. This self-sustaining loop is known as the geodynamo.

So you see that it is the permanent little magnets that iron atoms are which start the whole process and generate the measured magnetic field of the earth. This has very little to do with electromagnetic waves, as these are classical electric and magnetic fields.

You go on with:

Electromagnetic waves are caused by electric and magnetic waves,

There are no electric waves separate from magnetic waves. Waves mean varying behavior of some quantity in time. It has been observed and modeled that a varying electric field generates a magnetic field and a varying magnetic field generates an electric field. Under special conditions, an antenna for example, a self-sustained and sinusoidal — that is why it is called a wave — variation space versus time leaves the antenna and is a self-propelled wave with varying electric and magnetic fields, each sustaining the other.

so sense the earth supports both of these, electromagnetic waves can exist in the air, am I correct, if not please tell me how electromagnetic waves work.

The earth has nothing to do with it. In an antenna, it is electrons traveling sinusoidally up and down the antenna whose changing electric field generates a changing magnetic field and the self-propelled wave.

I have asked why don't electromagnetic waves need a vacuum to move through but the answer is to complicated,

This is how an em wave propagates in time

Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. This 3D animation shows a plane linearly polarized wave propagating from left to right. Note that the electric and magnetic fields in such a wave are in-phase with each other, reaching minima and maxima together

Light, the electromagnetic field, is described with very great accuracy by solutions of the Maxwell equations, one of which you see in the animation. A basic experimental fact is that these waves propagate in vacuum with velocity $c$. This was not explained, just accepted as a fact, since the Michelson Morley experiment showed that there was no medium on which light propagated, just the vacuum.

Until the quantum mechanical description of light was discovered, i.e. that light is composed out of zillions of photons. Photons are elementary particles which move with velocity $c$ in vacuum and form the macroscopic electromagnetic wave, as explained in my answer to your other question.

• If the electrons are moving up and down in the antenna then how does that travel out would it just stay near the antenna? – Gary Zenger Feb 28 '17 at 1:21
• It is an experimental fact that this motion generates the electromagnetic radiation which moves away with velocity c, as illustrated in the animation. The mathematical description with Maxwell's equations shows how this is described with accuracy. – anna v Feb 28 '17 at 4:25

From what I can gather, you are asking about how electromagnetic waves work, and also how the Earth contributes to electromagnetic forces with its own magnetic field. So I'll try to assist your understanding, though as others have noted, this may not be the best place for a question such as this.

Electromagnetic waves can be broken down into two types. The first is called near field electromagnetic waves, and the second is called far field electromagnetic waves. The electric force and the magnetic force apply to charged particles. When the particles are stationary, only the electric force applies. But when the particles move relative to one-another the magnetic force has an effect as well. Charges are both the source and the target of electric and magnetic forces.

So obviously, if you have a whole bunch of free-moving charges, initially stationary, then one particle is moved suddenly. Neglecting the magnetic force, the electric force causes nearby particles to move apart. Then, since they are moving, the magnetic force really comes into play, causing different force and different motion. From there, both electric and magnetic forces are in action. As the particles move about due to these forces, the original movement of these particle could be said to cause a wave motion throughout the whole group of charges. This wave is called a near-field electromagnetic wave.

The thing to note is that this "wave" is just caused by forces, and it has a speed because force has a speed. Forces cannot move faster than the speed of light - it is a law of nature, and a very interesting one at that. So the electric and magnetic forces can't affect things faster than light can move. They "travel".

The amazing thing about electromagnetic forces, though, is that they can become decoupled from their source. This is unlike most things that we know to cause forces. But when I move a charge, though near field interactions occur, as well the electric and magnetic forces become decoupled from that charge, and continue on in all directions. They still move at the speed of light, because they're forces. But they don't rely on their source. Rather, they only rely on each other - the electric force and the magnetic force, that is. This is another law of nature, and physics takes it as such. These electromagnetic forces, or waves, travelling out into space, are called far-field electromagnetic waves or electromagnetic radiation.

While near-field EM waves require a medium, with charged bodies to "conduct the wave" if you will, far-field EM forces/waves occur anywhere, including a vacuum. They move in the same way all forces "move" - by nature of the fact that they can't get anywhere instantly. If a planet is suddenly created next to you, it would take a finite amount of time for the gravity of that planet to actually produce force upon you. If you have a steel bar that goes out into the middle of the galaxy, and you give it a good push, the other side of that bar will not move for years, because force is not instantaneous.

Another interesting feature of EM radiation is the fact that the radiation requires energy (the ability to move charges in this case) to propagate, and this energy is taken from the source, so it cannot get the energy it radiates back, ever. This is a pretty bizarre but interesting effect.

Far-field EM waves are important for radio, and light, and other things you think of when thinking about electromagnetic waves. Near field stuff is used for NFC (near-field communication) between phones in close proximity, among other things.

As for the Earth's core, I can't speak on that, unfortunately. I simply don't know enough about it.

I truly hope I was of help in discussing this with you. If you have any questions or if anything was unclear, leave a comment and I'll get back to you.

Sam

• How would a charge just suddenly move? What would cause it to move and yes thank you most of it was helpful and made sense. – Gary Zenger Feb 28 '17 at 1:25
• A free, charged particle would move any time there's an electric force on it. All electric force is a result of charged particles, so a particle moves whenever a new charged particle gets close enough to have significant force. This is somewhat paradoxical, I suppose. There's no good way to actually have a stationary group of free charges and then suddenly introduce something new, as well. – Sam Gallagher Feb 28 '17 at 20:27
• In reality, particles are positioned relative to each other with batteries, thermionic emission, thermoelectric effects, induction, and other methods. They all, at their core, consist of free charged particles moving. For example, in a radio, we could have a battery connected to an oscillator which rapidly changes the direction of the current, forwards and back. The signal's changing current causes changing voltage (Ohm's law) and that voltage is applied to a large open-ended conductor. The conductor sees a rapidly changing voltage, causing near-field waves along the conductor. – Sam Gallagher Feb 28 '17 at 20:32
• Note that no current flows through this conductor, the antenna. The electric forces applied by the oscillating circuit, which you can measure using voltage, are the only things in the conductor. The thing is, these waves of force will reflect back at the metal-air interface, so antennas are always measured to be a fraction of the wavelength of the wave (frequency * speed of wave) for example 1/4 the wavelength for a 'dipole' antenna. Since you have charges moving, and the waves don't interfere destructively, the antenna will have higher levels of far-field radiation. – Sam Gallagher Feb 28 '17 at 20:37
• Remember that all charges that accelerate will emit far-field radiation. But typically they're all interfering with one-another, and reflecting all over the place, so they don't radiate as much as the antenna. This is not to say that the circuits don't radiate, though. They do, and that's why they have metal "tins" on top (google "RF PCB" and scroll until you find the metal lids on the boards). But that's a side-effect. The antenna is designed specifically to radiate a lot, by being proper length. All other conductors avoid that length. – Sam Gallagher Feb 28 '17 at 20:40