Question

Dante drew a diagram to show how a wire uses the magnetic field of a magnet to induce an electric current.

A wire connected to the red terminal on a grey box, which contains a white box with a needle pointing up. The wire is disconnected from the blue terminal on this box. The wire passes through a 3 sided trough with a bar magnet running on each side of the top inside of the trough. There the wire is labeled with a downward pointing arrow and the words Direction of movement of wire.

How can Dante correct the diagram?

He can move the wire upward instead of downward.
He can connect the wire to both ends of the ammeter.
He can change the wire from coiled to straight.
He can place the wire between the poles of the magnet and not move it.

Answer 1

Choose 1, 2 and 3. Option 4 is wrong.

Brief reasons:
- 2 (connect to both ammeter terminals): the circuit must be closed for a current to be measured.
- 3 (use a straight conductor): a single straight conductor moving through the magnetic gap is the usual way to show motional induction; a coiled tangle in the trough would not clearly cut flux the way shown.
- 1 (change the direction of motion if necessary): the conductor must move so that it cuts the magnetic flux (i.e. perpendicular to the field). If the original downward arrow has the wire moving along the field lines (so producing no emf), reversing the motion to cut the field (upwards or simply across the gap) corrects that.
- 4 is incorrect because a stationary wire in a steady magnetic field does not have an induced emf (no change of flux).