Physics Help

Discus: SAT/ACT Tests and Test Preparation: March 2004 Archive: Physics Help
 By Bcmz1234 (Bcmz1234) on Wednesday, March 03, 2004 - 11:42 am: Edit

O <---- You are looking at a circular loop of wire. You throw a bar magnet, north end first, through the center of the loop. As the magnet gets closer to the loop, a current would begin to flow around the loop. Its direction would be A clockwise or B clockwise.

Can someone please tell me the answer to this and the reasoning behind it?

 By Jszab (Jszab) on Wednesday, March 03, 2004 - 12:23 pm: Edit

Try Lenz principle, or right hand rule.

 By Bcmz1234 (Bcmz1234) on Wednesday, March 03, 2004 - 09:40 pm: Edit

Well the magnetic field lines would go straight through the ring, so the induced lines would have to come the opposite direction making the induced current go counterclockwise, right?

 By Korinfox (Korinfox) on Wednesday, March 03, 2004 - 10:25 pm: Edit

um...... I think it is clockwise... my reasoning is Lenz's law of course and the right hand rule that goes with it (it's basically a mathematical vector cross product)... anyway
ring O and bar magnet going into the screen north first
the velocity is into the screen so point your thumb towards your monitor
then the field is perpendicular to the direction of movement of the bar magnet, point out from the center on the north pole right?
so you do your cross product/right hand rule and so the current is induced out of your palm, and in a clockwise direction

 By Bcmz1234 (Bcmz1234) on Thursday, March 04, 2004 - 10:55 am: Edit

Alright, thanks.

 By Stanfordrulez (Stanfordrulez) on Sunday, March 07, 2004 - 04:23 am: Edit

Quote:

O <---- You are looking at a circular loop of wire. You throw a bar magnet, north end first, through the center of the loop. As the magnet gets closer to the loop, a current would begin to flow around the loop. Its direction would be A clockwise or B clockwise.

Can someone please tell me the answer to this and the reasoning behind it?

Well.
For me:
When the Magnet with its North end closes in on the loop, a current will be produced which'll oppose the motion of the magnet [Lenz's Rule]-- ie, a north pole'll be produced. A north pole is produced when current flows in the COUNTER-CLOCKWISE direction.

 By Stanfordrulez (Stanfordrulez) on Sunday, March 07, 2004 - 04:24 am: Edit

If it were clockwise, it would develop a south polarity and attract the magnet, in defiance of Lenz's law.

 By Korinfox (Korinfox) on Sunday, March 07, 2004 - 09:51 am: Edit

wait a second..... dammit using my right hand rules I still get clockwise.... but using my other right hand rule I get counter clock wise..... wtf??? hold on.... ok I'm killing myself here..... I know its a north pole rule and using my rule for north pole of a coil or wire (solenoid) I get counter clockwise.... but using my other rule I get clockwise.... ahhhhhhrg I'm pretty sure my right hand rules are correct though.... AHRRRRRGH although I believe the north pole rule, it would be clockwise if it were a non-convential circuit, in other words minus to plus....... AHHHRRRRG

 By Stanfordrulez (Stanfordrulez) on Sunday, March 07, 2004 - 11:37 am: Edit

Hey Kori-- I'm right, for sure
But. Even I've had problems with the Right Hand Rule. Thats why I don't use it !