22.1

Electromagnetic Induction

Student Notes

A current-carrying wire is surrounded by a magnetic field. The field is either into or out of the screen as shown in the simulation. A current can be induced in the nearby induction loop, and an ammeter detects the current. A graph shows the induced current as a function of time. You can adjust the current through the wire, and so change the magnetic flux through the induction loop. When the induced current is counter-clockwise in the loop the ammeter reading is positive. Similarly, a clockwise induced current corresponds to a negative ammeter reading.

1. | Initially the current in the wire is constant at 5 A. Why is the current in the loop zero?
2. | Use Lenz's law to predict the direction of the induced current when you change the current in the wire from 0 to 10 A. Check it out with the simulation.
3. | Use Lenz's law to predict the direction of the induced current when you change the current in the wire from 10 to 0 A. Check it out with the simulation.
4. | Use Lenz's law to predict the direction of the induced current when you change the current in the wire from 0 to -10 A. Check it out with the simulation.
5. | Change the current again from 0 to -10 A, but this time do it in a way that the magnitude of the induced current is larger than it was the last time. How can you accomplish this?

Self-test

How would you have to vary the current in the wire to achieve a square wave current pattern in the induction loop? A square wave is positive and constant for a time, then suddenly negative and constant for an equal time, then positive again, and so forth.

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