Detect Magnetic Vs. Electric fields.

[Flyndaran]

What's the difference? If you have one, don't you almost always have the other? Why does gurps give them as examples that stack linearly in cost 10+10?

[Bruno]

Well, one key difference is that electric fields are a lot simpler than magnetic ones. Seriously key.

"In physics, an electric field is the region of space surrounding electrically charged particles and time-varying magnetic fields." - wobbly magnetic fields can make electric fields, charged particles can make electric fields.

vs

"Magnetic fields are produced by moving electric charges and the intrinsic magnetic moments of elementary particles associated with a fundamental quantum property, their spin." and then you go down the quantum rabbit-hole.

[whswhs]

Originally Posted by Flyndaran

What's the difference? If you have one, don't you almost always have the other? Why does gurps give them as examples that stack linearly in cost 10+10?

A compass will respond to the Earth's magnetic field to point north; but it won't respond to a static electric field at all.

Touching an electroscope to an object with a static electric charge will produce a response; but it won't react to a static magnetic field at all.

The two phenomena, electricity and magnetism, were identified entirely separately, back in ancient Greece. They were seen as analogous and comparably mysterious in the Renaissance outburst of science and sorcery. But they weren't shown to be associated until around 1800, and they weren't actually unified until Maxwell. If they were almost always found together, it couldn't possibly have taken that long.

Bill Stoddard

[jeff_wilson]

Originally Posted by Flyndaran

What's the difference? If you have one, don't you almost always have the other? Why does gurps give them as examples that stack linearly in cost 10+10?

Everything with a charge has an electric field. Only if it moves wrt the observer is there a magnetic field.

[whswhs]

Originally Posted by jeff_wilson

Everything with a charge has an electric field. Only if it moves wrt the observer is there a magnetic field.

And if you have electrons moving along a metal wire, the charge of the electrons and the charge of the nuclei are equal, so at any macroscopic distance they cancel each other; but at least one of them is moving with respect to an outside observer. So the wire has an external magnetic field but no external electric field.

Bill Stoddard

[Anthony]

Originally Posted by whswhs

And if you have electrons moving along a metal wire, the charge of the electrons and the charge of the nuclei are equal, so at any macroscopic distance they cancel each other; but at least one of them is moving with respect to an outside observer. So the wire has an external magnetic field but no external electric field.

Nah, there's an electric field unless dealing with a superconductor -- you don't get a current without a voltage difference, and that's an electric field. Tends to be a very weak field, though.

[whswhs]

Originally Posted by Anthony

Nah, there's an electric field unless dealing with a superconductor -- you don't get a current without a voltage difference, and that's an electric field. Tends to be a very weak field, though.

Essentially negligible. It's not going to have macroscopic effects, unless you have insanely high voltage.

Bill Stoddard

[Flyndaran]

So what are some real world examples?
In gurps terms, please.
Is it if it can shock you it has an electric field, but if it can't and is still electromagnetic-y it will appear on detect magnetic fields?

[Jovus]

Originally Posted by Flyndaran

So what are some real world examples?
In gurps terms, please.
Is it if it can shock you it has an electric field, but if it can't and is still electromagnetic-y it will appear on detect magnetic fields?

Anything with a static charge will show up as an electric field but not a magnetic one. Possible examples:

van der Graaf generators
batteries
capacitors
storms
Faraday cages

Magnetic fields involve the movement of current. Examples of things that will throw up magnetic fields but not electric fields:

magnets
current flowing through a wire
non-leaky oscilloscopes

[Flyndaran]

That sounds like detect magnetic fields should cost less than detect electric fields in nearly every game.
Unless absolute direction: requires magnetic field could get subsumed into it for free.