In an ideal transformer, which statement is true about currents?

In an ideal transformer, which statement is true about currents?

• A. I_s = I_p
• B. I_s = (N_s/N_p) × I_p
• C. I_s = (N_p/N_s) × I_p
• D. I_s = (V_p/V_s) × I_p

Answer: (C)

In an ideal transformer, power is conserved, so the input power equals the output power: Vp Ip = Vs Is. This leads to Is = (Vp/Vs) Ip. Because the voltages are related to turns by Vp/Vs = Np/Ns, you get Is = (Np/Ns) Ip. This shows that the secondary current is inversely related to the turns ratio: if the primary has more turns than the secondary, the secondary current must be larger to keep power constant. The form using the turns ratio is the most direct way to express how currents relate, which is why it’s the best choice. Note that Is = (Vp/Vs) Ip is also valid, since Vp/Vs equals Np/Ns in an ideal transformer, but the current-focused expression with turns is the standard way to describe the relationship.

In an ideal transformer, power is conserved, so the input power equals the output power: Vp Ip = Vs Is. This leads to Is = (Vp/Vs) Ip. Because the voltages are related to turns by Vp/Vs = Np/Ns, you get Is = (Np/Ns) Ip. This shows that the secondary current is inversely related to the turns ratio: if the primary has more turns than the secondary, the secondary current must be larger to keep power constant.

The form using the turns ratio is the most direct way to express how currents relate, which is why it’s the best choice. Note that Is = (Vp/Vs) Ip is also valid, since Vp/Vs equals Np/Ns in an ideal transformer, but the current-focused expression with turns is the standard way to describe the relationship.