<p>A bar magnet (N at the top, S at the bottom) is moving downward, south pole first, toward a loop of wire. Which of the following best describes the current induced in the wire?
(A) Clockwise, as viewed from above
(B) Counterclockwise, as viewed from above
(C) The current alternates
(D) There is no current induced in the wire
(E) The direction of the current cannot be determined from the information given here</p>
<p>What is the answer?</p>
<p>Current is induced in the wire because of electromagnetic induction. There is a change in magnetic field linkage surrounding and through the loops of wire, there is relative motion by the magnet and the wire or simply because the magnetic field lines of the magnet cuts through the wire a potential difference is induced between the two ends of the wire.</p>
<p>According to Lenz’s Law the direction of the current should be such as that to oppose the change causing it. It should oppose the relative motion eating up some of the kinetic energy to be converted into electric potential energy, providing a newton third law pair force. This is done by the wire inducing a pole near the magnet in order to resist the movement of the magnet. This could be either a south or north pole.</p>
<p>By using the right hand grip rule (point your thumb into the direction of the north pole induced by the current or in the direction opposite of the south pole induced and the direction your fingers curl would be the direction of the current.</p>
<p>So now the answer should be clear.</p>
<p>Thank you for the thorough explanation. I get the answer B; counterclockwise. But in Sparknotes, it says it’s A. Which one is right?</p>
<p>It’s A.</p>
<p>The loop of wire doesn’t induce a north pole up, but rather a south pole. Like poles repel each other, there the magnet feels the resistance.
Using the right hand grip rule it indicates clockwise when seen from above.</p>
<p>I have a very similar question on my Princeton book. I’d say it’s the exact same question. But it says that as a magnet (N at top, S at bottom) approaches a loop from above, the flux keeps increasing downward, and so to oppose it (Lenz’s Law), we create an upward flux. Then according to the right hand rule, the current must flow counterclockwise.
How come? Either sparknotes is wrong, or my PR book is wrong…because as far as I can tell, there is no difference between the question on PR and the one on sparknotes.</p>