This a question that bothers me from a SAT Physics review book.

So in the question, there is a bar magnet with north pole up and south pole down going upwards through a loop of wire and (from my understanding) inducing a current from the emf created by change in magnetic flux.

The question asks what direction is the current and whether it changes direction. My teacher believes it will always be clockwise, but the answer from Princeton review says that it will first become clockwise, then switch to counterclockwise.

I personally think my teacher is right since the change in magnetic flux is in the same "direction" (NORTH pole approaching loop, and then SOUTH pole leaving loop), thus always generating a clockwise current.

So which is the correct answer? Any explanations would greatly help, thanks so much.


closed as off-topic by John Rennie, stafusa, sammy gerbil, ZeroTheHero, Sebastian Riese Jun 4 '18 at 11:04

This question appears to be off-topic. The users who voted to close gave this specific reason:

  • "Homework-like questions should ask about a specific physics concept and show some effort to work through the problem. We want our questions to be useful to the broader community, and to future users. See our meta site for more guidance on how to edit your question to make it better" – John Rennie, stafusa, ZeroTheHero
If this question can be reworded to fit the rules in the help center, please edit the question.



the change in magnetic flux is in the same "direction"

is incorrect. The magnetic flux starts off at zero, increases to a maximal value, and then decreases back to zero. This is impossible to achieve with a monotonic derivative, i.e. the rate of change of the flux needs to change sign partway through the interaction.


Not the answer you're looking for? Browse other questions tagged or ask your own question.