WAEC Physics 2014 Paper

Concept:A transformer works on the principle of mutual induction. The ratio of output voltage to input voltage is equal to the ratio of secondary turns to primary turns.Explanation:For an ideal transformer, the voltage ratio is given by:$$\frac{E_s}{E_p} = \frac{N_s}{N_p}$$Here, $E_p = 150 \, V$, $N_p = 400$ turns, and $N_s = 40$ turns.Substitute the given values:$$\frac{E_s}{150} = \frac{40}{400}$$Simplify the turns ratio:$$\frac{40}{400} = \frac{1}{10}$$Now solve for $E_s$:$$E_s = \frac{150 \times 40}{400}$$$$E_s = \frac{150}{10}$$$$E_s = 15 \, V$$Answer:The magnitude of the output voltage is $15 \, V$.Therefore, the correct option is D.