Primary power vs. load change — behavior in an ideal transformer: If the load current on the secondary increases, does the real power drawn by the primary remain the same?

Introduction / Context:
Transformers reflect load changes back to the primary. Understanding the dynamic between secondary load and primary input is crucial for power budgeting, fuse sizing, and efficiency calculations. If the secondary draws more power, the primary must supply more power (plus any losses) to maintain energy balance.

Given Data / Assumptions:

• Ideal or high-efficiency transformer.
• Voltage ratio set by turns ratio; primary supply voltage remains nominal.
• No internal regulation inherent to the transformer itself.

Concept / Approach:
In steady state, conservation of power dictates P_primary ≈ P_secondary/efficiency. As the secondary current increases (for the same secondary voltage), secondary real power rises. Therefore, the primary real power must also rise proportionally (ignoring minor changes due to voltage regulation and losses). It cannot “remain the same.”

Step-by-Step Solution:

Verification / Alternative check:
Measure input current as the secondary load resistor is decreased. The primary current increases correspondingly, showing higher input wattage on a wattmeter.

Why Other Options Are Wrong:
“Correct” contradicts power balance. Qualifiers about step-down, unity power factor, or voltage regulation do not change the fundamental energy conservation requirement.

Common Pitfalls:
Assuming the transformer itself regulates power; in reality, it only transforms voltage/current ratios and transfers power demanded by the load.

Final Answer:
Incorrect