Solenoid Q (1 Viewer)

[~TeLEpAtHeTiC~]

Originally posted by walla
that's right except that you would need to say an emf was induced in the first, not a current. a current by definition moves so "a current with nowhere to go" is not a current.

sorry..substitude EMF for current

 

[Farnarcle]

The way I see it is in the coil with no wire all the electrons got pushed to one end of the wire, and then wanted to spread out again, due to their similar charge. This created a LARGE replusion force to the magnet.

In the other one the electrons could keep moivng in a circuit, but there still would be a small 'back emf' that caused a smaller repulsion.

So the one with no wire moved away more.

 

[walla]

^
electrons don't repel magnets
currents do

 

[LadyMoon]

OKOK i agree with the whole explaination, but tell me this:
I said everything abt Faraday Lenz, induced current, magnetic field etc.
But....stupid me said in the second one a south pole is created at the end of the Solenoid, as a result it gets attracted to it.
I come home and look at the book it says it should have been north pole, and a south pole violates principle of conservation of energy.

How many do you think i can get out of the 5? (or was it 4?) would i lose 2 marks or 1.??
Help me out plz.

 

[dnt stop runnin]

i rekon u should lose only one......then again, depends wat the markers are like.....but one should be enough

 

[walla]

i doubt you would lose more than one, although possibly two if they don't think you understand lenz's law

 

[william]

there is a bracket after the solenoid said: (coils), so there must be emf produced in both coils. by lenz's law, they should be move to left.but I am not quite sure what is the effect that the second one has a more copper wire

 

[toknblackguy]

yep
i talked about the second one doing nothingm, cause it was an incomplete circuit and just an emf was induced
with second one, the induced emf gave rise to current to oppose..llenzs law..resulted in a north pole at the right, repelling and then the solenoid goes left

 

[walla]

william they don't both move to the left. while there is an emf induced in both, a current flows only in the second one. It is current, not emf, that makes them electromagnets, so only the second one moves.

 

[william]

Originally posted by toknblackguy
yep
i talked about the second one doing nothingm, cause it was an incomplete circuit and just an emf was induced
with second one, the induced emf gave rise to current to oppose..llenzs law..resulted in a north pole at the right, repelling and then the solenoid goes left

incomplete circuit? because there is no copper wire in the first one?

 

[pigs_can_fly]

eddy currents and induced currents are the same. only in a wire or coil of wire, the flow of charges is restricted to the wire (assuming it is connected to an external circuit), and so you get a current flowing. in a sheet conductor, currents are still induced like in the coil of wire, but because they have 'no where to go', they form swirling currents we call 'eddy currents' which have an associated magnetic field which combines to oppose the motion that caused them (lenz's law). so really, i don't see the distinction between eddy currents and normal currents, they're all just flows of charge. so in the first solenoid, you wouldn't say eddy currents are induced cos they just flow like a normal current. you might mention separation of charges however and perhaps an emf, but definitely not current. im pretty sure only the second one will move to the left, since a current will flow through it.

 

[Leon585]

[Please stop posting things like that or risk being banned - Ragerunner]

 

[pigs_can_fly]

thnx. i'll keep that in mind...

 

[freaking_out]

Originally posted by Leon585
[Please stop posting things like that or risk being banned - Ragerunner]

hey, what did he say?

 

[Shragga]

I screwed up in the test, but taking a second look, this is what I think the marks were looking for:
1. The first investigation creates no current (circuit not complete). Therefore, no magnetic field. Oesterd's law states that current (not EMF) generates magnetic field. Nothing happens.
2. The change in flux in second inv causes EMF to be generated in solenoid. But circuit is complete. Therefore, it becomes an electromagnet, with north pole adjacent to north pole of magnet, thus opposing the change in flux.
3. The solenoid is repelled to left, as it is free to move in a pendulum motion.
4. As the solenoid moves back due to gravity, change in flux occurs again, as a north pole is created again adjacent to the magnet. Considering the question emphasises that the magnet is strong, it is able to repel it again, such that it swings left and back, left and back, like a half-pendular motion.

I didnt say 4... I only said it would be repelled. Meh.

 

[ND]

I said the same, except on 4, i said that when the solenoid moves back due to gravity, while a current will be induced to counter the movement, the force due to gravity will prevail and it will soon come to rest at the lowest position.

 

[Adam]

Um, the first one is like a copper pipe is it not, and by my obsevations, a conductor slows down in a copper pipe, so there is a current being induced.