WAEC Physics 2012 Paper

Concept:Transmission loss depends on the square of the current, so reducing the current minimizes energy lost as heat.Explanation:For a fixed power output, $P = VI$.If the voltage $V$ is increased, the current $I$ decreases.Heat loss in transmission lines is given by $P_{\text{loss}} = I^2R$.A lower current therefore causes much smaller cable losses.Thus, transmitting alternating current at high voltage and low current is the most economical method over long distances.Answer:C. alternating current at high voltage and low current