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direction of the induced e.m.f

Say that magnetic flux with a positive value was passing through a coil.

The positive magnetic flux density was suddenly decreased to 0 and kept at 0 for a while.

Then the magnetic flux was decreased to a negative value during time t.

Would the induced e.m.f during the two intervals be in opposite direction? i.e. would one have a positive value and the other negative value?
Original post by Sang95
Say that magnetic flux with a positive value was passing through a coil.

The positive magnetic flux density was suddenly decreased to 0 and kept at 0 for a while.

Then the magnetic flux was decreased to a negative value during time t.

Would the induced e.m.f during the two intervals be in opposite direction? i.e. would one have a positive value and the other negative value?


Don't take my word as law on this; I suck at Electromagnetism/etc, and it's been a while, but just to give you something to go on...

Lenz's Law states that any induced EMF will be induced in a way such that it opposes the changes that cause its induction. Weird sentence, that's how I memorised it xD, either way, if a B field is high and a change is caused that reduces it, the result will be a current and hence EMF that acts in a manner that produces a magnetic field that attempts to bring back that high initial B field...

Here;
1.JPG

and

Attachment not found
Either way, hope I helped... to some extent? My diagrams are bad, I know. In any case, just think about Lenz' law and how the induced current must act in a manner that opposes the changes in magnetic flux causing it, i.e. to increase the B field when it is decreasing, etc.

Should help :smile:
2.JPG105.7KB
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Sang95
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Thanks but I'm just wondering if the induced e.m.f. would be in the same direction during both time intervals?
Original post by Sang95
Say that magnetic flux with a positive value was passing through a coil.

The positive magnetic flux density was suddenly decreased to 0 and kept at 0 for a while.

Then the magnetic flux was decreased to a negative value during time t.

Would the induced e.m.f during the two intervals be in opposite direction? i.e. would one have a positive value and the other negative value?


E=-dΦ/dt
In both cases Φ is decreasing. So dΦ/dt has the same sign in both cases and thus the EMF has the same direction in both cases.

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