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Question from 2002 HSC (1 Viewer)

helper

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If the rod was connected to a circuit and they asked you to label the direction of the current.

There is no conventional current at all in the diagram as shown which is part of what is wrong with your answer.
 

d_elmo

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shot number 2:

ok then is this question addressing lenz's law where we want the current thats induced to flow in such a way that the force exerted opposes the original change?
 

helper

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There is no current but an induced EMF.

As was answered before. There is a seperation of charges due to the changing magnetic flux.
This resulted in in the electrons moving to end X.

The direction of current is from high top low potential (+ve to -ve). So if an external circuit was to flow it would flow Y to X.
 

helper

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Using Right Hand Rule
Motion is up. Point thumb up in direction of motion indicating the way positive charges are moving.
Point Fingers from Left to Right. Field from N to S.

Palm is pointing into the page, so positives experience a force to End Y. So negatives experience a force towards end X.
As only electrons can move, they will move towards end X.
As there is no external circuit they will accumulate at end X making it negative.

This can be confirmed with Lenz's Law.
Thumb points in direction of positive charges, into Y.
Fingers point from N to S (Left to Right)
Palm points down confirming that the Force produced is opposing the motion.
 

BillyMak

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d_elmo said:
This is one of the easiest questions ive ever seen
Obviously not since your explanation is wrong. The only reason that your answer was correct is because you messed up twice and your messups cancled each other out.

Remember that the force acting on the rod must oppose it's original motion or else the rod would accelerate and it would be gaining kinetic energy from nowhere, so the force is DOWN. The palm of your hand faces down, thumb points into the page, meaning that end Y is more positive relative to X. X is the negative end.
 
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d_elmo

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Billy mak u obviously didnt read my second explanation because that is what i said anyway just get over it, im not perfect and i can actually admit that yes i was wrong please forgive me because your opinion of me means the world to me...
 

d_elmo

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by the way i guess u failed to notice that my second explanation was actually a question
 

ontherun

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kart racer i think ur qrong lenz's law duz have 2 do sumthing with this

the thing is based on lenz's law and the right hand grip rule
 

nit

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I'm not sure Lenz's law is at all useful in this case. That simply describes the force on the conductor which naturally opposes the original direction of motion. What we're interested in is the charge separation of the conductor.

I'm not sure about this, but I always thought that the negative end was the end from which electrons originated, not the end where they went. That meant I got Y as the answer. But then again I can see how charge build-up on the end X would mean that it would end up with a net negative charge on it as a result of this process.
 

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