A rectangular wire loop is connected to a sensitive ammeter, forming a complete circuit. The loop is pulled at constant speed from a region with no magnetic field into a wide region containing a uniform magnetic field. The field is at right angles to the plane of the loop. The ammeter deflects while the loop crosses the boundary of the field. It returns to zero when the loop is completely inside the field, even though the loop is still moving.
Which statement explains why the ammeter reading returns to zero?
The loop has stopped cutting field lines because its motion is now along the magnetic field lines.
The magnetic field through the whole loop is no longer changing, so no potential difference is induced.
The loop is moving at constant speed, so it has no kinetic energy available to transfer to the circuit.
The induced current has used up the mobile charge in the wire while the loop was entering the field.
92 exam-style questions on Edexcel GCSE Physics 13.1 Inducing a current, covering 13.1.1 Producing an electric current by induction, 13.1.2 Factors affecting the induced potential difference, 13.1.3 Alternators and dynamos, and 13.1.4 Microphones and loudspeakers. Each one has a worked solution and a mark scheme showing where the marks go.