A student designs a step-up transformer with an iron core. The input alternating current (a.c.) supply has an electromotive force (e.m.f.) of 24.0 V24.0\text{ V}24.0 V, and the expected output potential difference (p.d.) is 120 V120\text{ V}120 V.
State whether the primary or the secondary coil should have more turns, and calculate the ratio of the number of turns in the secondary coil to the primary coil, NsNp\frac{N_s}{N_p}NpNs.
Explain the function of the iron core in the transformer.
A device of resistance 150 Ω150\ \Omega150 Ω is connected across the secondary output. Assuming the transformer is 100%100\%100% efficient, calculate the input current to the transformer.
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.