JEE Main 2021 · 16 March · evening · Single correct · +4 / −1
For the given circuit, comment on the type of transformer used.
- (a) Auxiliary transformer
- (b) Step down transformer
- (c) Step-up transformer
- (d) Auto transformer
Answer and solution
Answer (c) Step-up transformer
Solution
Physics sir · 4 steps
Get the secondary voltage from the load's power and current, then compare it with the 220 V input.
- Secondary voltage. The load uses 60 W while drawing i_L = 0.11 A. Since P = V₂ i_L, the voltage across the secondary follows directly.
V₂ = P/i_L = 60/0.11 ≈ 545 V
- Compare with primary. The primary gets 220 V and the secondary gives about 545 V. The voltage has gone up, so N_S/N_P = V₂/V₁ ≈ 2.5, with more turns on the secondary.
- Check with current. For an ideal transformer, power in equals power out, so i₁ = 60/220 ≈ 0.27 A. That is more than 0.11 A: the current falls as the voltage rises, as it should.
- So. The output voltage is higher than the input voltage, so this is a step-up transformer, option (c).
The idea to keep. Find both voltages before you name a transformer. Step-up means a higher output voltage and a lower output current, because V₁ i₁ = V₂ i₂ for an ideal transformer.
Answer from the NTA final answer key. Solution by PrepWiser.