Ideal transformer power conservation.

Ideal transformer power conservation.

• A. Voltage on primary equals voltage on secondary.
• B. Power on primary approximately equals power on secondary; Vp/Vs = Np/Ns; I and V swap according to turns ratio.
• C. Power increases on secondary.
• D. Current on primary increases with voltage on secondary.

Answer: (B)

In an ideal transformer, power in equals power out, so Pp = Ps. The voltages scale with the turns ratio: Vp/Vs = Np/Ns. Because power is voltage times current, the currents must adjust inversely to keep the power the same: Ip/Is = Ns/Np. This means the transformer can step voltage up or down depending on the turns, while the current changes in the opposite direction to conserve energy (ignoring losses). That’s why the best description is that the primary power roughly equals the secondary power, the voltage ratio follows the turns ratio, and currents swap according to that same turns relationship to maintain Pp = Ps. The other statements either imply equal voltages, claim power increases, or misstate how the primary current relates to the secondary voltage.

In an ideal transformer, power in equals power out, so Pp = Ps. The voltages scale with the turns ratio: Vp/Vs = Np/Ns. Because power is voltage times current, the currents must adjust inversely to keep the power the same: Ip/Is = Ns/Np. This means the transformer can step voltage up or down depending on the turns, while the current changes in the opposite direction to conserve energy (ignoring losses).

That’s why the best description is that the primary power roughly equals the secondary power, the voltage ratio follows the turns ratio, and currents swap according to that same turns relationship to maintain Pp = Ps. The other statements either imply equal voltages, claim power increases, or misstate how the primary current relates to the secondary voltage.