A level physics question

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Question 9, why is the answer B and not C?

Reply 1

Brad12345678910

Original post by efsfsf\\eeeeeee

You have misread the mark scheme. The answer is C. The sheet experiences a change in magnetic flux as it enters the magnetic field, inducing emf, causing eddy currents to flow. The eddy currents cause a force to act, opposing the change causing it (Lenz's law), decelerating the sheet. The same concept applies when the sheet leaves the magnetic field.

Reply 2

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efsfsf\\eeeeeee

Original post by Brad12345678910

Wouldn't it accelerate the sheet after though if its opposing the motion?

Reply 3

Brad12345678910

Original post by efsfsf\\eeeeeee

Wouldn't it accelerate the sheet after though if its opposing the motion?

The force should always decelerate the sheet because of energy conservation. The kinetic energy lost when the sheet decelerates is transferred into electrical energy (eddy currents). Using the left hand rule also shows this to be true.