Define the ideal transformer relations between primary and secondary voltages and currents.

Define the ideal transformer relations between primary and secondary voltages and currents.

• A. V1/V2 = N2/N1; I1/I2 = N1/N2
• B. V1/V2 = N1/N2; I1/I2 = N2/N1
• C. V1 = V2; I1 = I2
• D. Power is not conserved in an ideal transformer

Answer: (B)

An ideal transformer scales voltages with the turns on the windings and currents in the opposite way so that power stays the same on both sides. The voltage ratio follows the turns ratio: V1/V2 = N1/N2. Because power must be conserved (V1 I1 = V2 I2), the currents scale inversely: I1/I2 = N2/N1. Put together, the primary-to-secondary voltage ratio is N1/N2 and the current ratio is N2/N1. This means if the primary has more turns than the secondary, the voltage is stepped down and the current is stepped up, keeping power constant. The other options misstate the turns relationship, imply equal voltages/currents, or deny power conservation, which isn’t the case for an ideal transformer.

An ideal transformer scales voltages with the turns on the windings and currents in the opposite way so that power stays the same on both sides. The voltage ratio follows the turns ratio: V1/V2 = N1/N2. Because power must be conserved (V1 I1 = V2 I2), the currents scale inversely: I1/I2 = N2/N1. Put together, the primary-to-secondary voltage ratio is N1/N2 and the current ratio is N2/N1. This means if the primary has more turns than the secondary, the voltage is stepped down and the current is stepped up, keeping power constant. The other options misstate the turns relationship, imply equal voltages/currents, or deny power conservation, which isn’t the case for an ideal transformer.