Primary side of a transformer is connected to 230 V, 50 Hz supply. Turns ratio of primary to secondary winding is 10: 1. Load resistance connected to secondary side is 46 Ω. The power consumed in it is :

Solution

Physics sir · 3 steps

First step the voltage down by the turns ratio, then V²/R gives the power in the load.

1. Secondary voltage. In an ideal transformer the voltage scales with the number of turns, so Vₛ/Vₚ = Nₛ/Nₚ. A 10:1 ratio cuts 230 V down to 23 V.

   Vₛ = Vₚ × Nₛ/Nₚ = 230 × 1/10 = 23 V

2. Power in load. The 230 V supply value is an rms value, so V²/R gives the average power directly: P = 23²/46 = 529/46 = 11.5 W. The 50 Hz frequency does not enter, because the load is purely resistive.
3. So. The load consumes 11.5 W, which is option (a).

The idea to keep. A transformer changes voltage in the turns ratio. After that, the load is just a resistor across the secondary voltage, so use P = Vₛ²/R with the rms value.

Answer from the NTA final answer key. Solution by PrepWiser.