Electric Field
Here is a simple way to build a device to detect an electric field.
Take a normal, air-filled balloon and tie a string to it. Hold it by the string. It should hang straight down, due to the gravitational force on it. However, by tapping the balloon you see that it only takes a little bit of a push to move the balloon around. If it experiences a constant force, for example due to a steady, light wind, the balloon string will point at an angle. The angle of the balloon string is essentially a force detector.
Rub the balloon against your hair (or borrow someone else's hair if you don't have enough). The balloon now has some charge on it. If you hold it by the string, it still hangs straight down most of the time. However, if there is an electric field present, the balloon will move somewhat in the direction of the electric field. The direction the string points indicates the direction of the electric field, and the deflection of the string from vertical indicates the strength of the electric field.
For example, if you hold the balloon near a wall, or near your sweater, it will likely start to deflect. This indicates that the wall or your sweater is creating an electric field. (This happens by electrostatic induction.)
If you walk around to different places, you find the direction and strength of the field is different everywhere. Even if you stay in one place, you may find that the direction and strength of the field is changing in time. By making a whole array of balloons all over a giant hall and watching all their deflections, you can map out the entire electric field.
You can visualize it as a bunch of arrows in space, the same way you might visualize the velocity of the air, which moves at different speeds in different directions everywhere. However, the arrows do not indicate anything is moving; they just indicate the deflection a balloon would have if it were there.
You can also visualize the electric field by imagining the arrows everywhere grow into each other, forming lines. For example, here's the wikipedia picture of the electric field lines for a dipole (one positive and one negative charge sitting nearby each other). Nothing is moving in this picture.
Magnetic Field
Magnetic fields are very much like electric fields.
Technically, your balloon could detect a magnetic field by moving it around and observing the forces on it, but that is not practical. A simple magnetic field detector is a compass. A compass points in the direction of the magnetic field.
You can also get an idea for how strong the magnetic field is by twisting the compass around in a circle. This will set the needle swinging back and forth. The faster the oscillations, the stronger the magnetic field.
We can visualize magnetic fields directly because little slivers of iron can act as tiny compasses. By spreading a bunch of them out around a magnet, we can see the outlines of the magnetic field lines. Here's the Wikipedia picture for this
:
This is a magnetic dipole, and as you can see it bears a strong resemblance to the electric dipole.
Relationship between Electric and Magnetic Fields
It turns out that electric and magnetic fields are related to each other. Charged particles create electric fields. However, if those same charges start moving, they create magnetic fields. If you try to use a compass near a wire carrying DC current, you'll see the needle deflected by the magnetic field created by the moving charges in the wire.
Further, electric fields and magnetic fields can create each other according to precise mathematical rules called Maxwell's equations. Any time an electric field changes in time, it creates a magnetic field that "curls" around it (loosely speaking - you have to learn vector calculus for the precise statement). Similarly, a changing magnetic field creates an electric field that curls around it in the same way. This is called "electromagnetic induction" (and is a different use of the word "induction" than when the balloon induced an electric field in the wall).
Electromagnetic Radiation
The rules for the relationship between electric and magnetic fields work out so that you can get propagating waves of electric and magnetic fields traveling through space. Very roughly speaking, the changing electric field creates a changing magnetic field, which creates a changing electric field, etc, and the whole thing propagates forward at the speed of light. To truly see how this works, you'll have to learn the math.
To make an electromagnetic wave, just take something with charge and shake it. If you take that balloon you rubbed against your hair and start shaking it back and forth, you're creating electromagnetic waves (their wavelength is hundreds of thousands of kilometers, though). If you could shake the balloon back and forth about a quadrillion times per second, you would actually see light emitted from the balloon. At slightly lower frequencies you could emit microwaves from it to cook your food or, lower still, listen to it on your radio.
As for what an electromagnetic wave is, it is just a changing electric and magnetic field. If an electromagnetic wave came past you, you could detect it with your balloon by watching the balloon vibrate back and forth, or with your compass in the same way. However, most electromagnetic waves have frequencies too high to notice with an instrument as coarse as a balloon or a compass. Instead, we detect electromagnetic waves with things like film, CCD's and antennas.
So I understand the electromagnetic spectrum -- electromagnetic
radiation is mediated by photons
Briefly, electromagnetic radiation is due to real (observable) photons; electric and magnetic force are due to virtual photon exchange.
The macroscopic electromagnetic wave phenomena we observe are due to an almost unimaginable number of photons, electromagnetic "quanta", coherently adding together.
This is where I get lost; I can't visualize how it works.
This topic is not something that one "groks" overnight or, if you're like me (an EE), over some period of years. It's a continuous process.
Just today, while driving to Lowe's, something I had been thinking a long time about in quantum field theory suddenly became very clear.
The fact is, no matter how many classes you take or books you read, much of the material must, like a great chili, "stew" for awhile before it's ready.
Best Answer
First, a magnetic field does no work. Induced electric fields by a magnetic field( for example a time changing magnetic field), produce work. See the discussion here: physics.stackexchange.com/questions/67826/… and look for Jim's comments on the accepted answer. Magnetic fields generate electric fields inside an object and that's how work is produce. Although macroscopically it may seem that magnetism is ding all the work it's not.
And may I ask why you cannot picture electromagnetism doing work? Let's mention first that the electric and magnetic fields do not exist completely alone. By Special Relativity considerations one shows that in an inertial frame were only one of the fields exist, in another both exist.
From the scope of classical electromagnetism( Maxwell equations) it's not so valid to discuss the existence of photons. Electromagnetic radiation is the propagation of time dependent coupled electromagnetic fields- by coupled I mean that one field has a phase relation with the other. This result comes from solving the Maxwell equations, the equations of motion for classic light.This radiation carries energy and momentum in the fields and these fields exert a force on object via a force called Lorentz force (https://en.wikipedia.org/wiki/Lorentz_force and https://en.wikipedia.org/wiki/Covariant_formulation_of_classical_electromagnetism).
So classical light can exert a force, but it's just to small to feel. When the light of the Sun heats you on a hot day, a force is exerted on your body on a molecular level, this force translate in work is the energy your body cells gain and so they warm up. You can also think of visible light of lasers, where a highly energetic beam concentrated can do real damage to an object or the case of gamma radiation that can damage your DNA.
If you now take quantum mechanical considerations you can think of light being quantized, but to do that properly one should quantize the electromagnetic field. A simpler approach is to treat the interacting particles( electrons for example) as quantum mechanical and the interaction between them taken as granted to be the electromagnetic potentials. Anyway, you may consider photons but these particles are not particles in the sense of a concrete classical body, since they describe a field.
Finally, I should mention once more that a body moved from an electric field( of a capacitor) could be seen from another frame of reference as moved by an electromagnetic field. And a body that is moved by magnetic field( a magnet) should be understood as a moving body because of the induced electric fields inside it.
Hope this helps.