Question

In a step-up transformer, if the voltage in the secondary is increased, then the current in the primary:

• A. Increases
• B. decreases
• C. does not change
• D. becomes zero

Hint:

Output power equals input power for an ideal transformer, so a higher secondary voltage on the same load draws more power.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept
For an ideal transformer, input power equals output power: \(V_{p}I_{p}=V_{s}I_{s}\).

Step 2: Effect
With a given load \(R\) on the secondary, the output power is \(\dfrac{V_{s}^{2}}{R}\). Raising \(V_{s}\) raises this power.

Step 3: Conclusion
With the supply voltage \(V_{p}\) fixed, \(I_{p}=\dfrac{V_{s}^{2}}{RV_{p}}\) increases.

Final Answer:
The primary current increases. \[ \boxed{\text{(A) }\text{Increases}} \]