Explain to me Electromagnetic Induction, EMF to be exact...

[QueenZ]

Hello, I am struggling to understand how electricity is generated in an AC generator... I know that there is a coil of wire and a magnet, and both of them have their own magnetic fields and as the magnet moves into the coil's magnetic field, it causes electrons to move in that coil. Well if that is right, then why is there no current flowing if the circuit is open? It only seems to be the case if the circuit is closed. I think it's called Electromotive force but how does it work? Does it literally PUSH the electrons? what difference does it make if we have a closed or an open circuit? If it PUSHES the electrons even in an open circuit then the wire would get hot and it would burn, no?

To illustrate this, I've put together 2 pictures, in which we have a closed circuit (we have current flowing) and in the other one we have the same thing but with an open circuit (I guess there's no current flowing there? why?).

Are the electrons moving or not in the second picture? why?

 

[Darkwood]

Finally something that makes sense....

so electrons never move in wires in ours homes either?

Speed of electricity - Wikipedia, the free encyclopedia
read this link it save me writing what it already covers...

 

[Silly Sausage]

You're obviously struggling here (no offence) Forget AC for the time being and study DC, basic circuit theory, electron drift, the list goes. Find some books on a more elementary level.


My first proper job, was working for a bloke who had his own computer firm back in early 80s, he started learning about computers from the Ladybird book, true. Admittedly, he was a Cambridge Maths graduate, so, reasonably clever!

 

[QueenZ]

Speed of electricity - Wikipedia, the free encyclopedia
read this link it save me writing what it already covers...

Already read it....

 

[Darkwood]

well, they move, but don't go anywhere. they oscillate, causing a movement of the electron field. the theory is far too deep for forum discussions. think of this. the surface of the earth is rotating at anything up to 1000mph. why are we not flung off?

sadly i culd give you an indepth explanation but i fear we will only go off on a tangent and il spend half the night on this thread lol...... but its quiz night t the local beer hole

 

[QueenZ]

You're obviously struggling here (no offence) Forget AC for the time being and study DC, basic circuit theory, electron drift, the list goes. Find some books on a more elementary level.


My first proper job, was working for a bloke who had his own computer firm back in early 80s, he started learning about computers from the Ladybird book, true. Admittedly, he was a Cambridge Maths graduate, so, reasonably clever!

I understand AC, PD, atoms and the basics... it's just this one area I'm struggling in...

 

[QueenZ]

sadly i culd give you an indepth explanation but i fear we will only go off on a tangent and il spend half the night on this thread lol

I have already looked into the quantum world, quantum entanglement etc. so go ahead...

 

[telectrix]

time for bed. said zebedee.

 

[Darkwood]

Already read it....

Well it was your opening post that suggested you hadn't read with the mention of electrons moving, but it should give you insight, il try explain it in everyday terms, you have 2 magnets one in each hand and you sweep the magnets passed each other close together and you will feel the force between them, its similar force thats acting on a quantum level to the electron field, if the magnet stayed still the electron field would just re-organise but by moving the magnet it can create a wave effect to the field.
If you want to understand again in everyday terms what happens with electrons and how the field moves then the best way to explain something like current in a.c. would be a straw full of a million electrons end to end all in a single file, (small straw) if you have a potential difference between the ends of the straw then the eletrons will want to go to the positive end so push 1 electron in the negative end at at the same instance the electron at the other end will fall out, as its ac the field reverses so the electron thats just fallen out gets push back in and instantly the original electron you pushed in drops back out.
Now the action of pushing the electron in and the electron at the far end was instant (electromagnetic field) but each electron has only moved back and forth and kept its position more or less.
In d.c. you keep pushing them in one end only so the propogation is the same (near light speed) but the electrons migrate slowly to positive in the order of mm per hour.


Hope this helps

 

[QueenZ]

time for bed. said zebedee.

you're right... :aureola:

 

[QueenZ]

Well it was your opening post that suggested you hadn't read with the mention of electrons moving, but it should give you insight, il try explain it in everyday terms, you have 2 magnets one in each hand and you sweep the magnets passed each other close together and you will feel the force between them, its similar force thats acting on a quantum level to the electron field, if the magnet stayed still the electron field would just re-organise but by moving the magnet it can create a wave effect to the field.
If you want to understand again in everyday terms what happens with electrons and how the field moves then the best way to explain something like current in a.c. would be a straw full of a million electrons end to end all in a single file, (small straw) if you have a potential difference between the ends of the straw then the eletrons will want to go to the positive end so push 1 electron in the negative end at at the same instance the electron at the other end will fall out, as its ac the field reverses so the electron thats just fallen out gets push back in and instantly the original electron you pushed in drops back out.
Now the action of pushing the electron in and the electron at the far end was instant (electromagnetic field) but each electron has only moved back and forth and kept its position more or less.
In d.c. you keep pushing them in one end only so the propogation is the same (near light speed) but the electrons migrate slowly to positive in the order of mm per hour.


Hope this helps

I'll read it a couple of times and try to get it...

 

[Knobhead]

How come this thread has got dumped in this section? It's got nothing to do with commercial/industrial at all.

 

[plugsandsparks]

Dunno, isn't there a GCSE physics forum somewhere this can go cos its doing my head in.

 

[Knobhead]

Pity there isn’t a skip section it could be dumped in!

 

[Darkwood]

Im on 3 physics forums, 2 quantum, and electrical is my side-line...... agree should be in electrical theory but if the question gets asked il do my best to answer although it wont improve his conduit bending its still feeding his desire to learn so nerrr!!!! :tounge_smile:

 

[Silly Sausage]

Im on 3 physics forums, 2 quantum, and electrical is my side-line...... agree should be in electrical theory but if the question gets asked il do my best to answer although it wont improve his conduit bending its still feeding his desire to learn so nerrr!!!! :tounge_smile:

Good for you mate. I love physics, quantum theory etc., but it is a bit pointless spouting such things to someone who can't grasp the basic concept of a simple circuit.
As for QT, what's the famous quote...'If you think you understand QT, you've no idea' something like that.
I'm sure you'll be able to enlighten me.