Hello Friends

I hope you all had good holidays (time-off sense, not to celebrate the Jew carpenter's supposed birthday).

I would greatly appreciate it if someone knowledgeable in the field of Physics can help me understand the shape and structure of the electromagnetic field. All I know is that there are short waves and long waves, and I've always thought of them as wavy arrows passing one another and not hitting each other.

But yesterday while in bed, I was watching this video by Prof. Richard Feynman and he says, they are NOT arrows going past each other, but 'fluctuations in the magnetic field' ... I'm not sure what he means .. I do however understand the rest of the video (really fascinating).

Because the way I had previously understood the electromagnetic field has been shattered (thanks Prof. Feynman) ... I am now confused. If right in this room I am sitting, I am getting so many electromagnetic waves (bouncing around the room) ... how is it that they do not interfere with each other !!

I hope my confusion on this matter is clear, and would love to be able to grasp this in a clear manner. Also please, please use simple, easy to understand explanations .. I am a n00b, but want to learn as much as I can about our wonderful universe before I rot.

Thank You.

Hmm I have so many more questions now

1. what are the coloured sheets at the bottom of the diagram ?
2. That K axis .. is that at 45 degrees between Z and Y ? or is it bang in the middle between X, Y and Z ?
3. What is the red wavy line and the blue wavy line ?
4. How is it that electromagnetic waves of different frequencies do not interfere with one another, even if they have the structure demonstrated in the diagram.

Chuck a pebble in a pond, then five seconds later throw another pebble in five feet away. Observe.

I live in an area with no ponds, and then even if there was a pond nearby, the British winter winds wouldn't leave the surface of the pond in peace for me to perform that little experiment.

Some answers to my previous questions about the diagram please.

Ciwan wrote:Hmm I have so many more questions now

1. what are the coloured sheets at the bottom of the diagram ?
2. That K axis .. is that at 45 degrees between Z and Y ? or is it bang in the middle between X, Y and Z ?
3. What is the red wavy line and the blue wavy line ?
4. How is it that electromagnetic waves of different frequencies do not interfere with one another, even if they have the structure demonstrated in the diagram.

k is a vector showing the direction the wave is moving in. It's a bit hard to tell from the diagram, but it looks like this is oriented bang in between the x, y and z axes, so if you projected it onto the xy plane, it would be at 45deg, same if you projected it on yz and zx axes.

The coloured sheets... well it looks like they're a set of imaginary planes through which the k vector cuts at right angles. So the E and B field at any point will lie in the plane through that point. So the E and B fields will be perpendicular to k.

The red wavy line traces the tip of the E vector and the blue one the tip of the B vector. What these vectors mean is.....if you had tiny electrically charged particles spread out through space, the E field would displace them by an amount shown by the E vector as it passes through.

The reason you can have zillions of radio transmissions through the same piece of space and receive them is the superposition principle. The waves do add up and subtract to form a composite signal, but the process is linear and at the radio receiver, by focusing on a specific frequency, you can re-extract your wanted signal from the superposed mush.

Thanks Twistor.

A few things, by B field .. you mean H field correct ? Also what do you mean when you say that the process is linear ?

Thanks

Ciwan wrote:Thanks Twistor.

A few things, by B field .. you mean H field correct ? Also what do you mean when you say that the process is linear ?

Thanks

B and H are related by a constant factor in vacuum, so yes, you can use either.

By linear, I mean that if I take two electromagnetic waves and allow them to propagate into the same area, the resultant E and B fields are got just by adding up the individual Es and Bs of the waves. There are no, for example, quadratic terms in the sum. E = E1+E2 and B = B1+B2.

The first thing you need to realise is that no-one, not even Stephen Hawking, really understands what electromagnetic waves are. If you want to achieve the extremely advanced, genius level ignorance that the experts have, you can dedicate yourself to multiple years of study.

Electromagnetic waves can be wave or particle, and can be a magnetic field collapsing into an electric field collapsing into...... and so on.

Or you can just think of them as very special waves.

Some things about these waves.

They travel through space at light speed - 300,000 kilometres per second.
The come in a wide range of sizes, called wavelengths, or frequencies. Very long waves, like radio waves, carry little energy. Very short waves, like gamma rays, carry lots of energy. That is why gamma rays can kill you, and radio waves cannot.

The longest waves, with the least energy are the kind of radio waves generated with very long aerials. Then come other radio waves, down to microwaves used in your microwave oven. By the time you get to microwaves, they have gained enough energy to heat water.

Then come light waves. Red is the longest wave with the least energy, and blue is the shortest with a lot more energy. Even shorter, with even more energy is ultraviolet, which can cause sunburn, such is its energy.

Shorter still is X-rays, which can penetrate your flesh. Then gamma rays, which are shortest of all with the most energy. A good dose of gamma rays can cause you to die from radiation.

Hope this helps. If you do not need to know the esoteric bits, then just imagine electromagnetic waves as special waves travelling through space. You will almost know as much as the experts. (Just joking.)

Thanks guys. I'm getting the feeling that if I really want to understand it I need to go and do a Physics degree

I mean 'curl' .. What do you mean by that ? Also .. Is the electromagnetic wave made of of Electrons (or some other fundamental particle) moving in a wavy-way through space ?

Ciwan
The EM wave will collapse into a particle, called a photon, under certain conditions. The duel particle/wave nature of EM radiation is another of those things that no-one really, truly understands. But they are not made of electrons.

Hmm I'll be lying to you if I said I now understand it.

The reason Electrons came to my mind and not Photons is:

1) I do not have a clue what a Photon is. It was never taught to us in High School GCSEs' Physics. All I know is that a Photon is a particle of light (first proposed by Einstein I believe). I'm not sure whether it has a Charge or not, I'm not sure whether it has a mass or not, and finally I'm assuming that it moves in straight line, since it is called a particle and not a 'wave'.

Point one is ignoring Quantum Mechanics, which shows us that Particles (e.g. Electrons) do sometime behave like waves

2) In another Prof. Feynman video, he tells us that the reason a Magnet has a pushing force, is because of the way the electrons spin. He said they spin in the same way, and that 'amplifies' their pushing or pulling force.

Now is Magnetisim different from the electro-Magnetism ?

Ciwan wrote:
Now is Magnetisim different from the electro-Magnetism ?

Not really, when you think of electromagnetism, you think of a current in a wire creating a magnetic field.

In a permanent magnet, there are also electron motions which are the equivalents of tiny currents. The orbital and spin motions of the electrons create this effect (although of course you mustn't literally think of the electron as a spinning ball of charge).

So how should I think of Electrons ?

Ciwan wrote::( So how should I think of Electrons ?

To be honest I don't really know. I don't have a picture in my mind when someone says "electron". The only pictures I can imagine are pictures of classical objects and an electron isn't one of those. It's a quantum mechanical object. Quantum mechanically, the electron is part of a system and the system has a "state" which has all the possible information about that system encoded in it. What you get when you make measurements on the electron is determined by the rules of quantum mechanics, which are defined mathematically.

You can try to picture it as a fuzzy cloud, but even that's not quite right, because under some circumstances electrons behave (to all intents and purposes) as point particles.

I don't think humans can picture electrons.

Thanks, I can't help but feel a little sad not being able to grasp the 'idea' of an electron !!

How do we know about their charges ? I assume our senses here also fail for Protons and Neutrons .. They too aren't little round balls right ?

So how do we know that an Electron (which we don't really know the looks of) has a negative charge ?

Thanks