Question

Which of these situations would generate electrical current in a wire? Check all that apply.

moving a magnet into a solenoid
moving a magnet out of a solenoid
holding a magnet steady inside a solenoid
holding a solenoid steady outside a magnet
moving a solenoid in a magnetic field

Answer 1

Correct answers:
- moving a magnet into a solenoid — Yes
- moving a magnet out of a solenoid — Yes
- holding a magnet steady inside a solenoid — No
- holding a solenoid steady outside a magnet — No
- moving a solenoid in a magnetic field — Yes (if the motion changes the magnetic flux through the coil)

Reason: Faraday’s law — an emf (and thus current, if the circuit is closed) is induced when the magnetic flux through the loop changes. Moving the magnet in or out changes the flux. If everything is truly steady the flux doesn’t change so no current. Moving the solenoid through a field will induce current whenever that motion changes the flux (for example moving into or out of the field, or changing orientation); motion in a perfectly uniform region that leaves the flux constant would not induce current.