Two fixed, insulated coils are wound close together but are not electrically connected. The first coil is connected to a cell and a switch. The second coil is connected to a sensitive ammeter, forming a complete circuit. When the switch is closed, the ammeter needle flicks to one side and then returns to zero, although the switch remains closed.
Which statement explains why the ammeter shows a current for only a moment?
The current in the first coil rises as the switch is closed, briefly changing the magnetic field through the second coil and inducing a potential difference.
The magnetic field exerts a motor-effect force on the fixed second coil, and the current stops because the coil cannot continue moving.
Closing the switch briefly joins the two circuits, so the cell drives a current through the ammeter only while the switch contacts are moving.
A steady current in the first coil produces no magnetic field, so the second coil receives no further energy after the switch closes.
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.