Which of the following statements correctly represents the relationships for an ideal transformer?

• A. Vp/Vs = Np/Ns and Ip/Is = Np/Ns
• B. Vp/Vs = Ns/Np and Ip/Is = Np/Ns
• C. Vp/Vs = Np/Ns and Is/Ip = Ns/Np
• D. Vp/Vs = Np/Ns and Ip/Is = Ns/Np; P_in = P_out; Vp Ip = Vs Is

Answer: (D)

The test is about how an ideal transformer relates voltages, currents, and turns. In an ideal transformer, the output voltage is set by the turns ratio: Vp/Vs = Np/Ns. To conserve power (no losses), the input power equals the output power, so Vp Ip = Vs Is. From that, the current ratio must be the inverse of the voltage ratio: Ip/Is = Vs/Vp = Ns/Np (and equivalently Is/Ip = Np/Ns). This means if the secondary has more turns than the primary, it steps up the voltage and steps down the current, and vice versa.

The statement that matches these relationships also explicitly states the power balance P_in = P_out (Vp Ip = Vs Is), reinforcing the same idea. The other options mix up the voltage and current ratios or omit the power conservation relation, so they don’t align with how an ideal transformer truly behaves.