Solenoid Q (2 Viewers)

Constip8edSkunk · Oct 31, 2003

What was the question? Did the question say the coils were originally moving in pendulum motion or were they stationary... think i might have misread the q.....

+:: $i[Q]u3 ::+ · Oct 31, 2003

i'm pretty sure they were stationary... the question was like... they're allowed to move in penduluum motion...
did u talk about the pendulum bt? cuz all i said was the second one gets pushed to the left.. i never said it came back down again.... (?)

Calisc · Oct 31, 2003

I did the same thing as you $i

new1 · Oct 31, 2003

they were stationary hanging on a string (as i recall)

one was made into a circuit with the copper wire, the other not

the one that was had a corrent induced, that one made a magnetic field and pushed itself away from the magnet. the other one with no circuit din do shit

Constip8edSkunk · Oct 31, 2003

hmm crap i thought it read that they were moving then you put the magnets in

4 marks *kapooof*

walla · Oct 31, 2003

hmmmm no i didn't say it swung back down...though obviously it would.....i did mention that the effect only occurred when there was relative motion though so hopefully its implied

Mathematician · Oct 31, 2003

...

I am pretty sure and better not be wrong that the force acts on both of them. The external circuit just allows a current to flow (driven by the induced emf) but its not what creates the force.

Lenz's law is stated as "a change in flux gives rise to an induced emf , the direction of which is determined by the opposing force" or something... So not the current. We use the opposing force to determine the direction of the induced emf or current if there is a circuit.

So in both cases there is an opposite pole causing repulsion. But i was stupid i thought that it would move to the left but then thought of other things i read in textbooks that were confusing me and thought the repulsion would somehow cause it to swing more .. ????/

Are they going to kill me for this??? i said there was a repulsive force.

dnt stop runnin · Oct 31, 2003

do both of them swing or just the second one coz thecircuit is completed with the copper wire.....whereas the first one isnt??.......or am i just talking crap?

walla · Oct 31, 2003

Re: ...

Originally posted by Mathematician
I am pretty sure and better not be wrong that the force acts on both of them. The external circuit just allows a current to flow (driven by the induced emf) but its not what creates the force.

Lenz's law is stated as "a change in flux gives rise to an induced emf , the direction of which is determined by the opposing force" or something... So not the current. We use the opposing force to determine the direction of the induced emf or current if there is a circuit.

So in both cases there is an opposite pole causing repulsion. But i was stupid i thought that it would move to the left but then thought of other things i read in textbooks that were confusing me and thought the repulsion would somehow cause it to spin more .. ????/

Are they going to kill me for this??? i said there was a repulsive force.

yes there is an emf in both
but current is what makes an electromagnet, not just emf, so only the second one repels

Mathematician · Oct 31, 2003

..

oh shit ur right...

But then again think of when a magnet is dropped in the aluminium pipe..

Yeah current makes the electromagnet when u wanna magnetise a ferromagnetic material..

BUT the whole think about induction is the force isnt due to it being an electromagnet (become magnetised due to relative motion).. its all about the eddy currents which create the force..

so yeah i think im right

+:: $i[Q]u3 ::+ · Oct 31, 2003

in the first one.. there's no force.. because there's no current induced...
you have to have a closed circuit to induce a current.

it's like when u crank a generator with teh switch open and the swtich closed.. it's harder with it closed..c uz the current can flow.. yeah?

Mathematician · Oct 31, 2003

..

NO and ill be real pissed if im wrong cause i went real crap in other areas. But u too will be pissed if ur wrong.. lol\
Oh shit ur right im talking about eddy currents causing the poles to be generated but to have them in the first place it needs to be closed...

NOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOOO

walla · Oct 31, 2003

hahaha we aren't wrong
no eddy currents are being induced, its a coil not an aluminium pipe
there's emf but nowhere for the electrons to go hence no current, no force.

+:: $i[Q]u3 ::+ · Oct 31, 2003

how do u have a current if there's nowhere for the current to go?!?!!? a current is the flow of electrons. i = dq/dt.
okay so there may be eddy currents.. but they mean nothing in a solenoid question... (??) lol.. am i gonna get owned sometime soon?

Constip8edSkunk · Oct 31, 2003

i just want to read the question again

mikehunt · Oct 31, 2003

Originally posted by +:: $i[Q]u3 ::+
how do u have a current if there's nowhere for the current to go?!?!!? a current is the flow of electrons. i = dq/dt.
okay so there may be eddy currents.. but they mean nothing in a solenoid question... (??) lol.. am i gonna get owned sometime soon?

no cause your right

Jimmoi · Oct 31, 2003

Originally posted by walla
hahaha we aren't wrong
no eddy currents are being induced, its a coil not an aluminium pipe
there's emf but nowhere for the electrons to go hence no current, no force.

Who ever said eddy currents are only produced in pipes or disks?

There are eddy currents and there will be an opposition in the change of flux. I thought eddy currents are allowed to be formed in any conductor?

Jimmoi

My2Sense

Bannanafish · Oct 31, 2003

yes i wrote eddy currents for investigation 1

eddy currents are induced wheneever there is no circuit, period

+:: $i[Q]u3 ::+ · Oct 31, 2003

yeah.. okay.. what i'm saying is..
even if there were eddy currents in the first solenoid.. there isnt a net current thru the wire coil of the solenoid.. so you don't get the magnetic flux that repels the magnet. hmm... am i being too obscure...
ahh well~~~ it's history =) let's all take a drink and sit back.. and study for chem~... =P (boo to the ppl who have alredy finished...)

smeyo · Oct 31, 2003

oh shit i forgot to talk about motion, stupid me i talked about nothing happening in the first but would in the second, just forgot to say exactly what....

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