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Energy transfer in electromagnetic induction 
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#73
Jan813, 08:05 AM

P: 37

Can we not increase the energy transferred initially by increasing the number of turns in the coil. More turns mean more current flowing in the coil. 


#74
Jan813, 10:17 AM

HW Helper
P: 3,443

This goes back to the point before. I think DaleSpam's answer was: "Think about the field generated by the induced current in the first turn. How does that affect the total field seen by the second turn. My hint is that the equation:
[tex]\displaystyle{\varepsilon}=N \frac{d \Phi}{dt} [/tex] Uses a lot of assumptions, and if you break those assumptions, you cannot expect the equation to give correct results. Edit: actually, it doesn't use a lot of assumptions, but the simple case of increasing number of turns to increase the current through the coil does introduce assumptions. Another Edit: and generally, it is assumptions used along with this equation that have caused the problems in this thread. For example, the assumption "that the magnetic field at the magnet and at the coil is approximately the same" is often used with this equation, but this assumption becomes false when the magnet and coil are far away from each other. 


#75
Jan813, 10:54 AM

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#76
Jan813, 11:09 AM

P: 37




#77
Jan813, 01:05 PM

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P: 16,981

If each dot represents the energy extracted by a coil with i turns then it is both true that "there is a limit to the energy that can be transferred" and "we can increase the energy transferred by increasing the number of turns". 


#78
Jan913, 11:56 AM

P: 37

Is this because the successive turns in the coil are linked to lesser magnetic flux? 


#79
Jan913, 12:39 PM

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P: 16,981

Yes, it is because each turn reduces the flux seen by the other turns. This can be seen through the superposition principle.
Suppose that you have two turns, consider them to be two separate loops. There is a current in loop A which creates a field which opposes the change in the external field. By superposition the field seen by loop B is the sum of the field from loop A and the external field, which is less than the change in the external field. So the current induced in B is a function of the external field and the current induced in A where current in A reduces the induced current in B. Then, to consider the loops as separate turns in a single coil simply equate the current in A to the current in B. 


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