 Ask Remember Me? Yusf Posts: 197, Reputation: 3 Junior Member #1 Nov 11, 2016, 08:13 PM
Work done in rotating a current carrying loop through a magnetic field
No real problem with calcukation but I am thinking that If the rotation is 460 degrees, then the work done is equal to the work done in rotating it 460 minus 360 equals 100 degrees. Right? ebaines Posts: 12,132, Reputation: 1307 Expert #2 Nov 12, 2016, 09:42 AM
This would imply that you could continue to rotate the loop in the magnetic field with no extra work required above the level required to turn it the first 360 degrees. If the loop is driving a current through a resistance, then this would mean free energy. What do you think? Yusf Posts: 197, Reputation: 3 Junior Member #3 Nov 12, 2016, 10:22 AM
Well, I thought from work done in normal sense. Work done is the dot product of force and displacement. So of I move a fridge 3m above the ground, the work done will be 3*weight. If I let it down by 1m, the work done will be -1w. So the net work done is 2w. Which equals force times displacement.
Now in this case the work done in first half cycle in equal to negative work done by second half. So the net work is equal to... zero.. (in one complete rotation)
*fingers crossed ebaines Posts: 12,132, Reputation: 1307 Expert #4 Nov 14, 2016, 06:44 AM
I see your point. Without knowing what the circuit is that the generator is connected to it's impossible to say whether work is performed as the coil rotates or not. A noted if there is a resistive load, which resists current flow in both directions, then the loop performs work regardless of which way the current flows. The analogy would be pushing a rock across a floor against friction - it doesn't matter which way you push the rock work is always being done on the rock. But it's not a resistive load, but instead the coil is connected to a battery such that it acts as a generator to charge the battery for half its cycle and becomes a motor driven by the battery for the second half of its cycle, then I would agree with you. Yusf Posts: 197, Reputation: 3 Junior Member #5 Nov 14, 2016, 07:51 AM
Aaaaah! I see. :) Thanks.

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