Question

An electric current is produced using a bar magnet and a solenoid.

Which changes will cause a decrease in the electric current produced? Check all that apply.

using more wire loops in the solenoid
using fewer wire loops in the solenoid
using a stronger magnet
moving the solenoid instead of the magnet
moving the magnet more slowly

Answer 1

Correct answers:
- using fewer wire loops in the solenoid
- moving the magnet more slowly

Reason: Faraday’s law gives emf = −N dΦ/dt (N = number of turns, Φ = magnetic flux). Current is proportional to the induced emf, so reducing N or reducing the rate of change of flux (by moving the magnet more slowly) decreases the current. Using more loops or a stronger magnet increases emf; moving the solenoid instead of the magnet (with the same relative speed) produces the same emf.