Question

You have a piece of copper (conductivity = 6.0*10^7 Ω^-1m^-1) wire 26 cm long and 2.0 mm in diameter and a bar magnet with a magnetic dipole moment of 0.75 Am^2. You decide you’re going to make use of induction to make some current flow in the wire.

First, you pull the copper wire into a circular loop. Then you hold the bar magnet 15 cm above the center of the loop, parallel to the loop so that there is no magnetic flux. Very quickly (over about 0.2 seconds), you rotate the magnet so that the north pole is facing toward the loop of wire, then hold the magnet at rest in this position.

What is the average current induced in the wire during the 0.2 seconds you rotate the magnet?
 


In what direction is this current? Justify your answer in words.

What is the average current induced in the next 0.2 seconds? Justify your answer in words.

Hint: Start with the induction problem to find the induced emf from the change in flux. Then, think back to Unit 3 and Ohm’s Law.

Answer 1

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