A 24 V, 48 W lamp is properly connected to the secondary of a step-down transformer, whose primary i

Question

A 24 V, 48 W lamp is properly connected to the secondary of a step-down transformer, whose primary is connected to an AC mains of 120 V. Assuming the transformer is ideal, what is the current drawn by the primary winding?

Professor PC Thomas Classes · Answer

(c) : For an ideal transformer, there is no power loss, meaning input power equals output power ($P_p = P_s$). The power consumed by the lamp at the secondary is $P_s = 48$ W. Therefore, the primary power $P_p = V_p I_p$ must also be 48 W. Since the primary voltage is $V_p = 120$ V, the primary current is $I_p = 48 / 120 = 0.4$ A.