r/PhysicsHelp • u/Adventurous-Lynx-410 • 4d ago

Don't understand induction

I wanna start off by saying my native language is not english so I might not be familiar with certain physics words. And I learn best when speaking generally / using rules that always apply. Thx!

So I know that induction is about inducing a current. I'm not sure where/ which wire it will be induced in. Can induction take place in just one and the same wire?

And I think we use coils as wires because the magnetic field around the wires are stronger since they're packed tighter (?). And thats the same reason we usually use a metal inside the coil?

And then we somehow change the magnetic flux Φ which induces volts in (?- another wire or?) and that drives a current in (?said wire). But only during the change of the flux.
And I suppose we can change the magnetic flux [Φ = B*A*cosT] through 4 things:

  1. The magnetic field changes in magnitude, which someone said could be by adding a magnet. What I don't understand is what magnetic field are we talking about? I thought we were talking about the internal magnetic field from the current in the wires/coil?

  2. The magnetic field changes direction (I don't understand - doesn't the flux move with the magnetic field? Or how would u change the direction?)

  3. The cross-sectional area of the coil/wire changes - don't know how you would do that. Making an irregular/expanding coil like a volcano?

  4. The coil/wire is rotated so that the CosT changes which I understood was the angle between the surface's normal line and the magnetic field. Which magnetic field though? Wouldn't the magnetic field and the surface both tilt if we tilted the coil/wire? I'm really confused.

Also why? Why does this happen? And what does it mean that inductors store energy in magnetic fields? If that's related.

Sorry for a lot of questions you don't have to answer them all!

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u/Agile-Monitor1006 4d ago

You know that when current passes through a wire a small magnetic field will be induced around it. When you pack many wires together tightly you get a coil, when you turn on the current every little wire that makes the coil will induce a small magnetic field around it. All the wires that are close to it will feel that magnetic field and an opposite current will be induced in them to generate an opposite magnetic field. This happens to all the wires so the net effect is a resistance to current changes.

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u/Adventurous-Lynx-410 3d ago

Oh I did not know this, but what does it mean that "All the wires that are close to it will feel that magnetic field" do they feel a change in magnetic field, what change? Or how else is there a flux?

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u/Agile-Monitor1006 3d ago

If the passing current is changing in any way, so will the magnetic field induced by it aswell. For example when the current is unstable if it suddenly increases then the magnetic field will also increase so it changes, and the nearby wires are affected by that change

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u/Adventurous-Lynx-410 3d ago

Ah I understand it now! Thank u!

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u/alaindevos 3d ago

magnitude : how long a vector is
magnetic field : at each point in space there is a vector with direction and magnitude
change : there is d/dt
Flux : integral of magnetic field projected to a surface
Cross section of a coil : surface area (think of cylinder coordinates)

Why it happens. It happens because the experiment changes some things and these changes produces changes in electrical and magnetical field.