TRANSFORMERS AND NATIONAL GRIDS

3 marks · Normal

A section of the National Grid transmits 2000 kW of electrical power at 400,000 V.

(a)

Calculate the current in the transmission line.

[2 marks]

(b)

Explain why this high voltage is used with reference to energy loss.

[1 mark]

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) 5 A

(b) —

Common mistakes: Confusing kW and W units; Not converting units before calculation

Show mark scheme and worked solution

Marking points

M1 (a) · 1 mark · Substitutes power and voltage into I = P / V with correct units.

A1 (a) · 1 mark · Correct calculation of current to 5 A (accept 5 A or 5.0 A within rounding).

B1 (b) · 1 mark · Explains that high voltage results in lower current, leading to reduced energy loss as heat.

Worked solution

(a) Power (P) = 2000 kW = 2,000,000 W; Voltage (V) = 400,000 V

(b) A high voltage means the current in the cables is much lower for the same power. Lower current means less energy is lost as heat (since heat loss depends on current squared).