A bicycle wheel turns a dynamo connected to a lamp. The rider keeps the wheel turning at a constant speed.
One lead to the lamp is then disconnected, opening the circuit. The rider continues to turn the wheel at the same speed.
Which statement explains the effect on the driving power needed from the rider?
Less driving power is needed because no induced current flows to produce a magnetic field that opposes the rotation.
More driving power is needed because the greater circuit resistance causes a larger induced current in the dynamo.
Less driving power is needed because the dynamo no longer induces a potential difference once the circuit is open.
The same driving power is needed because the dynamo induces the same potential difference at the same wheel speed.
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.