TRANSFORMERS AND NATIONAL GRIDS
4 marks · NormalElectricity generated at a power station must travel long distances before it reaches homes and factories.
Describe the effect a step-up transformer has on current and voltage when used in the National Grid.
Explain why using step-up transformers is important for reducing energy losses in transmission lines.
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(a) Increases voltage, decreases current
(b) Lower current reduces heating/energy losses in cables (as losses depend on current squared).
Common mistakes: Saying only 'increases voltage' with no reference to current; Saying 'reducing voltage reduces losses'
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Marking points
B1 (a) · 1 mark · States voltage increases (or is stepped up)
B2 (a) · 1 mark · States current decreases (or is stepped down)
M1 (b) · 1 mark · Links reduced current to reduced energy/heat losses
A1 (b) · 1 mark · Mentions power loss depends on current squared (I^2R loss) or gives a clear scientific reason
Worked solution
a) A step-up transformer increases the voltage and decreases the current in the transmission lines.
b) Lowering the current reduces energy lost as heat in the wires, because power loss due to resistance is given by .