An electric toothbrush is charged wirelessly by placing it on its charging dock.
When the charging dock is switched on, there is an alternating current (a.c.) in the primary coil located inside the dock. A secondary coil is inside the handle of the toothbrush.
Explain how an electric current is produced in this secondary coil.
The maximum energy stored in the battery of the electric toothbrush is 0.005 kWh.
Show that this maximum energy is 1.8 × 104 J.
The charging dock has a useful output power of 2.5 W. The manufacturer claims that the battery can be charged to 60% capacity in less than 90 minutes90\text{ minutes}90 minutes.
Show that this claim is true.
275 exam-style questions on CIE IGCSE Physics 4.5 Electromagnetic effects, covering 4.5.1a Electromagnetic induction, 4.5.1b Direction of an induced e.m.f., 4.5.2 The a.c. generator, 4.5.3a Magnetic effect of a current and its applications, 4.5.3b Strength and direction of the field around wires and solenoids, 4.5.4a Force on a current-carrying conductor, 4.5.4b Force on beams of charged particles, 4.5.5 The d.c. motor, 4.5.6a Construction and operation of a transformer, 4.5.6b Turns ratio and current in a transformer, and 4.5.6c High-voltage transmission of electricity. Each one has a worked solution and a mark scheme showing where the marks go.