In an ideal transformer, if Vs > Vp, the secondary current Is compared to the primary current Ip: it decreases.

In an ideal transformer, if Vs > Vp, the secondary current Is compared to the primary current Ip: it decreases.

• A. Increases
• B. Decreases
• C. Remains the same
• D. Becomes zero

Answer: (B)

Power balance in an ideal transformer means Vp Ip = Vs Is, so the currents scale inversely with the voltages. The voltage ratio Vs/Vp equals the turns ratio Ns/Np. When Vs is greater than Vp, the turns ratio is greater than one, and to keep power the same, the secondary current must be smaller than the primary current. In fact, Is = (Vp/Vs) Ip, which is less than Ip when Vs > Vp. So the secondary current decreases relative to the primary.

Power balance in an ideal transformer means Vp Ip = Vs Is, so the currents scale inversely with the voltages. The voltage ratio Vs/Vp equals the turns ratio Ns/Np. When Vs is greater than Vp, the turns ratio is greater than one, and to keep power the same, the secondary current must be smaller than the primary current. In fact, Is = (Vp/Vs) Ip, which is less than Ip when Vs > Vp. So the secondary current decreases relative to the primary.