Question

Julia produces a 2 mA current by moving the south pole of a bar magnet into a solenoid. The solenoid contains 150 loops of wire.

Which change should Julia make to generate a larger current?

moving the magnet slower
using more loops of wire in the coil
using the north pole of the magnet
setting the magnet down in the solenoid

Answer 1

Using more loops of wire in the coil.

Reason: Faraday's law says the induced emf = -N dΦ/dt, so increasing the number of turns N increases the induced emf (and therefore the induced current). Moving the magnet slower or setting it down reduces or stops the change in flux (reducing current). Using the north versus south pole only changes the direction of the induced current, not its magnitude.