# help needed in Electronmagnetic fild

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#1

Hi can anyone explain why the answer is like this and how to analyze the direction of the current in this question? Thanks!

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5 years ago
#2
Do you know how to apply RHR?
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#3
(Original post by jsMath)
Do you know how to apply RHR?
Yes I do, but as the direction of the movement and the field lines do not change, why does the current change in direction and why there is no current at position2? Thanks for your help.

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5 years ago
#4
Please accept my apologies for the delay, I have been sick for 5 days and I can't see well, the screen in blurry , so expect a lot of typographical errors Think of this question in terms of vector calculusYou have a lot of useful information both is the wordings and the graph.There does not exist current in the 2nd position that the square magnetic metal passes due to several reasons:Let me give you a simple trick using the RHR:what does it mean the direction of the ammeter at position 1 is clockwise and at position three anticlockwise?This tells you that your forces are canceling out at position 2.

This is clear from the maxwell's equations shown in the figure
What the equations are saying is that if you move from position 1 to 3 the rate of change of B is increasing. Maxwell's surface integral is telling you that there is an increase in the the rate of change of A. That implies your electric field is increasing or you may think of it in terms of emf at basic levels in which you can easily derive from the closed loop integral. So the potential will be high at the third position, it is like kicking the ball and the ball accelerates.

But at position 2 the flux is constant so no rate of change, hence it would be a region for potential forces cancelling each other out.

To be continued feel a bit tired can't concentrate...
1
#5
(Original post by jsMath)
Please accept my apologies for the delay, I have been sick for 5 days and I can't see well, the screen in blurry , so expect a lot of typographical errors Think of this question in terms of vector calculusYou have a lot of useful information both is the wordings and the graph.There does not exist current in the 2nd position that the square magnetic metal passes due to several reasons:Let me give you a simple trick using the RHR:what does it mean the direction of the ammeter at position 1 is clockwise and at position three anticlockwise?This tells you that your forces are canceling out at position 2.

This is clear from the maxwell's equations shown in the figure
What the equations are saying is that if you move from position 1 to 3 the rate of change of B is increasing. Maxwell's surface integral is telling you that there is an increase in the the rate of change of A. That implies your electric field is increasing or you may think of it in terms of emf at basic levels in which you can easily derive from the closed loop integral. So the potential will be high at the third position, it is like kicking the ball and the ball accelerates.

But at position 2 the flux is constant so no rate of change, hence it would be a region for potential forces cancelling each other out.

To be continued feel a bit tired can't concentrate...
Thanks so much for the detailed explanation! Could you tell me how can I know if the current is clockwise or unti-clockwise? Thanks.
0
5 years ago
#6
(Original post by 123321123)
Yes I do, but as the direction of the movement and the field lines do not change, why does the current change in direction and why there is no current at position2? Thanks for your help.

Posted from TSR Mobile
That's because in position 1 the current in frond end of the "circuit" is going from R to Q, and if you follow this current you would see that this current is also going from P to S. But in position 3 more than half of the frond end of the circuit is outside the magnetic field and so the only part of the circuit affected by the magnetic field is P to S end of the circuit, in which the current must follow from S to P (using the right hand rule), which was from P to S initially (because the front end of the circuit was affected by the magnetic field. Hope this does explain why there is no current flowing in position 2.

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#7
That's because in position 1 the current in frond end of the "circuit" is going from R to Q, and if you follow this current you would see that this current is also going from P to S. But in position 3 more than half of the frond end of the circuit is outside the magnetic field and so the only part of the circuit affected by the magnetic field is P to S end of the circuit, in which the current must follow from S to P (using the right hand rule), which was from P to S initially (because the front end of the circuit was affected by the magnetic field. Hope this does explain why there is no current flowing in position 2.

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What does frond end mean?
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5 years ago
#8
(Original post by 123321123)
What does frond end mean?
Sorry, I meant to say front end.

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#9
Sorry, I meant to say front end.

Posted from TSR Mobile
Ok I understand now. Thanks so much !

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