JAMB Physics 2015 Paper

Concept:Efficiency of a transformer is the ratio of useful power output to total power input.Explanation:The transformer transfers electrical power from the primary coil to the secondary coil.Useful power output is the power developed in the secondary coil, $P_s$.Total power input is the power supplied to the primary coil, $P_p$.Thus, efficiency is given by:$$Efficiency = \frac{P_s}{P_p} \times 100\%$$This means efficiency depends on power, not on voltage, current, or number of turns directly.Therefore, the correct statement is:$$Efficiency = \frac{\text{power developed in the secondary coil}}{\text{power supplied to the primary coil}} \times 100\%$$Answer:Option D.