TRANSFORMERS AND NATIONAL GRIDS
4 marks · NormalElectricity is transmitted over long distances from power stations to towns.
Explain in detail, using scientific ideas about current and voltage, how transformers help to reduce energy loss during this transmission.
Describe what happens to the current in the transmission wires when a step-up transformer increases the voltage.
Explain why this change in current is important for energy loss.
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) The current in the wires decreases when the transformer increases the voltage.
(b) Lower current causes less energy to be lost as heat since energy loss in cables is proportional to the square of the current.
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · States correctly that current decreases as voltage increases (step-up transformer).
B2 (a) · 1 mark · Mentions transmission wires explicitly.
B3 (b) · 1 mark · Explains less current means less energy lost.
B4 (b) · 1 mark · States heat lost is proportional to current squared (I^2R losses).
Worked solution
(a) When a step-up transformer increases the voltage, the current in the transmission wires decreases.
(b) This is important because lower current means less energy is lost as heat in the wires. The energy lost as heat is proportional to the square of the current (I^2R).