Mistake in TBR in Ch. 8

[brood910]

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In the first passage of the review questions section (not practice exams section), the answer to question #4 "for the circuit in Figure 21, which way does the induced current flow?" is counterclockwise. This contradicts with what the guy says in this video at the end:

http://www.youtube.com/watch?v=qWu82nJS42I&lc=JvRFHPhwzQWYTK-jiwl6TrD2nUiskrpH1j2I3Li3vcY

Could you please tell me which is correct?
I thought the induced current would be clockwise since area is the one that is changing to oppose the change of the magnetic flux, not the magnetic field..

 

[milski]

Let's consider the flux to be positive when the B field is into the page. When bar moves to the right, the area increases and the flux will increase as well. From Lenz's law, the current generated will try to preserve the flux as it was, which means that you will get current which generates negative flux. That's the same as flux generated by B fields out of the page. From the right hand rule, you need counterclockwise current to generate field out of the page - the answer is A.

The guy in the video does something different - he is not moving the bar but is changing the B field to zero. In his case the flux actually decreases and the current will be in the opposite direction.

 

[brood910]

Let's consider the flux to be positive when the B field is into the page. When bar moves to the right, the area increases and the flux will increase as well. From Lenz's law, the current generated will try to preserve the flux as it was, which means that you will get current which generates negative flux. That's the same as flux generated by B fields out of the page. From the right hand rule, you need counterclockwise current to generate field out of the page - the answer is A.

The guy in the video does something different - he is not moving the bar but is changing the B field to zero. In his case the flux actually decreases and the current will be in the opposite direction.

I just realized that by watching the vid again lol.
Thanks for the clarification.