Electromagnetism
5 marks · EasyA transformer is used in a small wind turbine system to supply electricity from the generator to a farmhouse.
Describe how a transformer works, including its main parts.
State why an alternating current (a.c.) is necessary for a transformer to work.
Explain how using a transformer in a National Grid system helps reduce energy losses during transmission.
Work this out on paper, then compare with the answer and worked solution below. With a free account you can submit written answers for marking.
Show answer
(a) A transformer has two coils (primary and secondary) wrapped around a soft iron core. A changing current in the primary coil creates a changing magnetic field, which induces a voltage in the secondary coil.
(b) A.c. is needed because only a changing magnetic field induces a current in the secondary coil.
(c) A transformer increases the voltage and decreases the current, so less energy is lost as heat in the transmission wires.
Common mistakes: Describing d.c. transformers as functional; Omitting the need for a changing magnetic field
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States transformer consists of two coils and a core.
B2 (a) · 1 mark · Describes how magnetic field changes induce voltage in the secondary.
B3 (b) · 1 mark · States that a.c. is necessary to create a changing magnetic field (not d.c.).
B4 (c) · 1 mark · States that transformer increases voltage and reduces current for transmission.
B5 (c) · 1 mark · Mentions energy (heat) loss is reduced when current is lower.
Worked solution
a) A transformer works by having a primary coil and a secondary coil wound around a soft iron core. When an alternating current flows in the primary coil, it produces a changing magnetic field in the core. This changing magnetic field passes through the secondary coil, inducing a voltage in it.
b) Alternating current is necessary because it produces a changing magnetic field. Only a changing magnetic field can induce a voltage in the secondary coil, as in electromagnetic induction. Direct current (d.c.) does not change and so will not work.
c) Using a transformer in the National Grid allows the voltage to be stepped up for transmission, which decreases the current in the cables. Lower currents mean less energy is lost as heat in the cable resistance, making electricity transmission more efficient.