A step-down transformer reduces secondary voltage; in the ideal case, what happens to the secondary current?

A step-down transformer reduces secondary voltage; in the ideal case, what happens to the secondary current?

• A. Reduces secondary current
• B. Remains constant
• C. Increases secondary current
• D. Becomes zero

Answer: (C)

In an ideal transformer, power in equals power out (Vp × Ip = Vs × Is). When the transformer steps voltage down, the secondary voltage Vs is smaller than the primary voltage Vp. To keep the same power, the current on the secondary side must rise so that Vs × Is matches Vp × Ip. Mathematically, Is = (Np/Ns) × Ip. For a step-down, the turns ratio Np/Ns is greater than 1, so the secondary current must increase. For a quick check: if the primary delivers 120 V at 1 A (120 W) and the secondary is 12 V, then to deliver the same 120 W, Is must be 120/12 = 10 A, which is higher than the primary current. This is why the secondary current increases in an ideal step-down transformer. The other options would violate power balance: the current doesn’t stay constant, doesn’t drop to zero, and doesn’t decrease.

In an ideal transformer, power in equals power out (Vp × Ip = Vs × Is). When the transformer steps voltage down, the secondary voltage Vs is smaller than the primary voltage Vp. To keep the same power, the current on the secondary side must rise so that Vs × Is matches Vp × Ip. Mathematically, Is = (Np/Ns) × Ip. For a step-down, the turns ratio Np/Ns is greater than 1, so the secondary current must increase.

For a quick check: if the primary delivers 120 V at 1 A (120 W) and the secondary is 12 V, then to deliver the same 120 W, Is must be 120/12 = 10 A, which is higher than the primary current. This is why the secondary current increases in an ideal step-down transformer.

The other options would violate power balance: the current doesn’t stay constant, doesn’t drop to zero, and doesn’t decrease.