TRANSFORMERS AND NATIONAL GRIDS
4 marks · NormalA village receives electricity from a National Grid. The voltage on the transmission cables is 132,000 V.
Give two reasons why a step-down transformer is needed before the electricity enters homes.
The step-down transformer reduces the voltage to 230 V. Explain what happens to the current in the secondary coil compared to the primary coil, assuming no energy is lost.
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.
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(a) The voltage is too high for use in homes; it is dangerous and will damage equipment.
(b) As the transformer reduces the voltage, the current in the secondary coil increases (for equal power).
Show mark scheme and worked solution
Marking points
B1 (a) · 1 mark · Reference to safety or danger from high voltages.
B2 (a) · 1 mark · Reference to damaging appliances or unsuitability for home use.
B3 (b) · 1 mark · States current increases in secondary coil.
B4 (b) · 1 mark · References constant power (V x I = constant if 100% efficient).
Worked solution
(a) The voltage on the transmission lines is far too high for domestic use; it is unsafe and would damage appliances.
(b) The step-down transformer reduces voltage and increases current in the secondary coil as power remains the same (V x I = constant).