Changing magnetic fields produce electric fields, and thus can induce current in a loop of wire. The direction and amount of current depend on several factors, which you can investigate in this experiment.

Objective

1. Use electromagnetic induction to determine the way in which a large solenoid is wound (i.e. counterclockwise/clockwise, starting from which connector)

Resources

• Solenoid
• Magnets
• Wires, alligator clips
• Galvanometer
• Battery
• Large (~10K) resistor

Background

A wire loop with N turns that bounds an area A that has a changing magnetic field passing through it will have an induced EMF equal to \mathcal{E}=-N\frac{\partial}{\partial t} \int \vec{B}\cdot d\vec{A} = -N\frac{d\Phi_B}{dt}

The direction of the EMF in the loop depends on the way the magnetic field is changing. Lenz’s Law says that the direction of the induced current creates an induced magnetic field that opposes the direction of change of the external field.

Guideposts/Hints

• Forming test cases may help you arrive at your answer, for example: “If the solenoid is wound counterclockwise starting from this connector, then when the North end of the magnet is moved toward this end of the solenoid..”
• When current flows into the positive terminal of the ammeter, should the needle deflect in a positive or negative direction? The battery and resistor might help you be certain of your answer.
• Your result in this experiment is not simply a number, but several connected statements about the solenoid. Make sure your result and the reasoning leading to it are complete and make sense – you may want to read it back to your partners to be sure.