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GR0177 #42
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Problem
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This problem is still being typed. |
Electromagnetism }Faraday Law
Faraday's law suggests that the current inducted opposes the changing field. (This is also known as Lenz Law). It acts something like an electromagnetic inertia.
Since the middle loop is moving towards the observer, the loop A feels an increasing current. Loop A will thus compensate with a current that acts to decrease the field-change; this current is counter-clockwise by the right-hand rule.
Since the middle loop is moving away from loop B, loop B will want to increase its magnetic field, and thus its current is in the same direction as the middle loop.
Only choice (C) works.
(One can immediately cancel out all but choices (A) and (B) from just a conceptual understanding of Lenz Law.)
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Comments |
memorial
2010-05-31 21:26:29 | "the loop A feels an increasing current" ? Do you mean magnetic flux?
|  | istezamer
2009-10-13 00:04:52 | I loved the word "Electromagnetic Inertia"!! it really describes what's going on !
Albert
2009-10-28 03:21:31 |
Yeah, nice term it is, Electromagnetic Inertia. Did you come up with it yourself Yosun? Good!
Someone said, strange gestures? Well, we physicists are known for that, aren't we? We do it all our lives :)
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| | kroner
2009-10-06 14:29:26 | Approximately 70 minutes into the test, all of the test takers inexplicably begin staring at their hands while making strange gestures. | | ramparts
2009-09-05 07:59:15 | A very useful thing to know (this was pointed out by a user in a problem on the 96 test) is that wires with current in the same direction attract, and wires with current in the opposite directions repel. So that with Lenz's law makes this problem a snap - the middle loop will induce a repelling current in A, and an attracting one in B, in an effort to restore the original state. | | tat747
2006-10-02 08:37:40 | I think there is a typo here. You can cancel out choices (A) and (B), based on a conceptual understanding of Lenz's Law...
Also, the current induced in Loop A will be CLOCK-WISE, thus, choice (C). |  |
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