please help for electromag - past hsc multiple choice!

[worldno1]

hi!

can anyone explain why the answer is D? would A not have any effect?
is this whole question related to eddy currents OR electromagnetic induction?

[zhudiac]

Hi,
Correct me if I'm wrong, but in the diagram, the coil of copper wire is not complete- therefore there is not complete circuit. Thus it must be D; as by completing the circuit, it allows the changing B-field to cause induce an opposing current in coil (according to Lenz's Law) so as to oppose the change in flux, causing a force to be exerted opposing the motion; slowing the pendulum down.
You are correct in that this is electromagnetic induction; due to the movement of the pendulum, there is a change in magnetic field density over a change in time, thus there is emf generated in the coil.

A is incorrect as the circuit is incomplete- a stronger B field will not change that fact.
Not sure about B and C tbh, but not likely as this is a electromagnetic induction question, although it could be all that pendulum stuff in the old syllabus.

[jamonwindeyer]

^ Welcome to the forums zhudiac! Killer first post, you're bang on the money - The coil isn't joined at the ends, so no complete path for the current to flow