TRANSFORMERS AND NATIONAL GRIDS
3 marks · NormalExplain, using scientific ideas, why it would be inefficient and impractical to transmit electricity at low voltage but high current.
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Transmitting electricity at low voltage and high current would cause much greater energy loss as heat in the wires (since power lost is proportional to current squared), making transmission inefficient and requiring much thicker cables.
Common mistakes: Incorrectly stating low voltage is more efficient
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Marking points
B1 · 1 mark · States large amounts of energy would be lost as heat.
B2 · 1 mark · Correctly references that power lost is proportional to current squared (I^2R loss).
B3 · 1 mark · Mentions impracticality (would need very thick cables or much more expensive infrastructure).
Worked solution
If electricity were transmitted at low voltage and high current, the current in the wires would be large. Energy lost as heat (P=I^2R) would be much higher, making the process inefficient. Cables would have to be much thicker to reduce resistance, increasing cost and difficulty.