The Direction and magnitude of current in the inductor

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  • #1
hidemi
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Homework Statement:
The diagram (see attachment) shows an inductor that is part of a circuit. The direction of the emf induced in the inductor is indicated. Which of the following is possible?

A. The current is constant and rightward
B. The current is constant and leftward
C. The current is increasing and rightward
D. The current is increasing and leftward
E. None of the above

The answer is D.
Relevant Equations:
ε = -L* dI/dt
I understand that the current is going rightward because of the negative sign in the equation above, but why is the current increasing not decreasing?
The current doesn't stay constant because it changes with the time based upon the equation above again.
 

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Answers and Replies

  • #2
tech99
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Homework Statement:: The diagram (see attachment) shows an inductor that is part of a circuit. The direction of the emf induced in the inductor is indicated. Which of the following is possible?

A. The current is constant and rightward
B. The current is constant and leftward
C. The current is increasing and rightward
D. The current is increasing and leftward
E. None of the above

The answer is D.
Relevant Equations:: ε = -L* dI/dt

I understand that the current is going rightward because of the negative sign in the equation above, but why is the current increasing not decreasing?
The current doesn't stay constant because it changes with the time based upon the equation above again.
A good way to understand inductors is to impress a known current (for instance, using a high series resistance) and see what voltage obtains. In the example shown, the voltage acts to the right. You only have options for "current increasing", making dI/dt is positive. As L is also positive, e opposes the current direction by flowing to the left.
 
  • #3
hidemi
208
36
A good way to understand inductors is to impress a known current (for instance, using a high series resistance) and see what voltage obtains. In the example shown, the voltage acts to the right. You only have options for "current increasing", making dI/dt is positive. As L is also positive, e opposes the current direction by flowing to the left.
Thank you so much.
 

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