# Magnetic Fields of batteries

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1. Apr 4, 2015

### MaterSammichM

1. I have heard that if you take 4 batteries and 2 non-coated wires, and run the wires + to -, with current flowing in opposing directions, with the wires in close proximity, that a magnetic field will be created between the 2 wires. Is this true?
2. Since photons have no charge, is there any interaction between magnetic waves and photons?
3. If you were to take a piece of magnetic shielding of sufficient length and wrap it around the circumference of one end of a cylindrical magnet, since the N/S fields would no longer be able to "close the loop", what would happen to the fields?

2. Apr 4, 2015

3. Apr 5, 2015

### Staff: Mentor

Magnetic waves and photons are the exact same thing. The magnetic and electric fields are united under one electromagnetic field, so waves in this field are known as electromagnetic waves. Photons are how electromagnetic waves interacts with matter.

Magnetic field lines always exist in closed loops. You cannot stop this. I believe magnetic shielding just makes the loops follow along the inside of the material.

4. Apr 5, 2015

### MaterSammichM

Please explain how magnetic waves and photons are the same thing; as I understand it, photons are "packets of light with no charge" that propagate away from passing electrons.

5. Apr 5, 2015

### Staff: Mentor

There is no such thing as a magnetic wave. There are only electromagnetic waves. Photons are how this EM wave interacts with matter. In other words, if an EM wave passes an object it will interact with this object only in quantized, discrete 'chunks' of energy which we have labeled as photons. Your camera sensor in your cell phone works because the incoming EM waves (light) deposit enough energy all at once in the form of a photon to knock an electron out of one area of the pixel and into another, where it is stored until read by the camera. A bright source of light puts off higher amplitude EM waves, which interact with the sensor via a greater number of photons over time, than a dimmer light source.

Does all that make sense?

6. Apr 5, 2015

Not yet

7. Apr 5, 2015

### Staff: Mentor

Okay. Let's start simple then. When I say that magnetic waves don't exist, only electromagnetic waves exist, do you know why? Do you understand the difference?

8. Apr 5, 2015

9. Apr 5, 2015

### Staff: Mentor

Well, I can try to explain the basics, but don't expect to understand fully without really getting into the subject on your own. Give me little bit to come up with something.

10. Apr 5, 2015

### MaterSammichM

I do understand beyond the basics, but what you are saying does not match conventional instruction

11. Apr 5, 2015

### Staff: Mentor

Okay. Do you know about electromagnetic induction and how a varying magnetic field creates an electric field?

12. Apr 5, 2015

### MaterSammichM

Yes

13. Apr 5, 2015

### MaterSammichM

Where yopu lost me is when you said, "Magnetic waves and photons are the exact same thing."

14. Apr 5, 2015

### Staff: Mentor

I can explain that, but first I need to make sure you understand that magnetic waves don't exist by themselves. Wherever you have a magnetic wave you also have an electric wave, and we call the whole thing an electromagnetic wave.

15. Apr 5, 2015

### MaterSammichM

16. Apr 5, 2015

### Staff: Mentor

Well, it's just like I originally explained. EM waves interact with matter not in a continous manner, but in a discrete way, transferring energy in packets or bundles. The amount of energy in each bundle is given by the relation: e=hv, where h is planck's constant and v is the frequency of the electromagnetic wave.

The common way of interpreting this is that an EM wave is composed of particles that we call 'photons'. This is semi-true. Photons are not particles like most people would think of. You can't stop one and do things to it like you can with an electron. It's more accurate to say that photons are quantized packets of energy. In other words, an EM wave comes in, interacts with something, and then moves on, losing energy in exact multiples of hv.

So when I say that photons and magnetic waves are the same thing, I mean that you can't separate the two. Where you have an EM wave interacting with something you have photons. They are, in essence, the exact same thing.

17. Apr 5, 2015

### Staff: Mentor

Another way to say it is that an electromagnetic wave is the classical limit of a large number of photons. Just as an electromagnetic wave carries energy and momentum and can transfer it to matter, so does a photon. They are the classical and quantum descriptions of the electromagnetic interaction.

18. Apr 5, 2015

### MaterSammichM

Thanks Drakkith, that helped clarify it perfectly. It would have helped if I had added "electro" to my OP.
Dale, you got me there... If a photon has no +/- charge, what energy is it transferring? Kinetic?

19. Apr 5, 2015

### Staff: Mentor

Electromagnetic energy. Kinetic energy or other forms of energy can be changed into electromagnetic energy and vice versa.

20. Apr 5, 2015

### MaterSammichM

Okay, so this may sound stupid, but when considering a basic neodymium magnet, what do you say are the particles(?) behind the forces?

21. Apr 5, 2015

### Staff: Mentor

I wouldn't use particles at all. The magnet has enough particles that a classical description is fine and there is no need or benefit to using quantum mechanics.

22. Apr 5, 2015

### MaterSammichM

okay, but what name are you giving them?

23. Apr 5, 2015

### Staff: Mentor

The photon is the force-carrier particle of the electromagnetic force, so it would be the photon. But we're getting deep into the realm of Quantum Electrodynamics and virtual particles, which will NOT make sense for you at this time.

24. Apr 6, 2015

### vanhees71

It's very misleading to think about photons as classical particles. They are very far from that. They even do not have anything like a position in the literal sense. It's also misleading to try to understand relativistic quantum field theory, and that's the only way to understand what photons mean properly, without a sound basis in classical relativistic field theory, and electrodynamics is the paradigmatic example and the only one describing physical phenomena (the only other one is gravity, but that demands even general relativity).

Next, you should get familiar with the fully relativistic description of electromagnetic phenomena. Maxwell's equations, which are nothing than the most simple possible field equations for a massless spin-1 field with electric charge-current distributions as sources. From the relativistic point of view, and that's the only consistent view on electromagnetic phenomena you can have, there is no electric or magnetic field by themselves but only one electromagnetic field as a whole. What you call "electric" and "magnetic" field are components of the electromagnetic field (which is relativistically represented by an antisymmetric 2nd-rank tensor field in four-dimensional Minkowski space-time) from the point of view of a given inertial reference frame.

E.g., the electromagnetic field of a permanent magnet is static and thus has in the rest frame of the magnet (and only there!) only magnetic components. If you move wrt. to the magnet you necessarily have both electric and magnetic field components. If you move with constant velocity, it's a static electromagnetic field.

Electromagnetic wave fields have always both electric and magnetic field components from any frame of reference. There's no static solution for the electromagnetic field that looks "wavy" in any way. This was one of the unsolved puzzles of the 19th century, because if you could move with the speed of light along an electromagnetic wave, you'd expect from a naive non-relativistic analysis based on the Galilei space-time structure, that there was such a solution of Maxwell's equations, supposed the Maxwell equations were invariant under Galilei transformations, when changing from one inertial frame to another. But that is not the case, and this brought after many years of struggle by some of the most clever physicists Einstein to the conclusion that Galilean space-time is not the fully correct description of space-time, which lead him to the development of Special Relativity in 1905.