Transformers problems
- 1. In a certain loaded transformer, the secondary voltage is one-fourth the primary voltage. The secondary current is
Options- A. one-fourth the primary current
- B. four times the primary current
- C. equal to the primary current
- D. one-fourth the primary current and equal to the primary current Discuss
Correct Answer: four times the primary current
- 2. To step 110 V ac down to 20 V ac, the turns ratio must be
Options- A. 5.5
- B. 18
- C. 0.18
- D. 0.018 Discuss
Correct Answer: 0.18
Explanation:
Vp/Vs = Np/Ns
Vs = (Ns/Np)Vp
We required turns ratio i.e., (Ns/Np)
= Vs/Vp
= 20/110
= 0.181818182
[Note: p - primary; s - secondary]
For step down transfer, the turns ratio will be less than 1.
For simulation: Step-Down Transformer Circuit Simulator.
Vs = (Ns/Np)Vp
We required turns ratio i.e., (Ns/Np)
= Vs/Vp
= 20/110
= 0.181818182
[Note: p - primary; s - secondary]
For step down transfer, the turns ratio will be less than 1.
For simulation: Step-Down Transformer Circuit Simulator.
- 3. When a 200 Ω load resistor is connected across the secondary winding of a transformer with a turns ratio of 4, the source "sees" a reflective load of
Options- A. 50 Ω
- B. 12.5 Ω
- C. 800 Ω
- D. 0 Ω Discuss
Correct Answer: 12.5 Ω
- 4. What kVA rating is required for a transformer that must handle a maximum load current of 8 A with a secondary voltage of 2 kV?
Options- A. 4 kVA
- B. 0.25 kVA
- C. 16 kVA
- D. 8 kVA Discuss
Correct Answer: 16 kVA
- 5. The primary winding of a transformer has 110 V ac across it. What is the secondary voltage if the turns ratio is 8?
Options- A. 8.8 V
- B. 88 V
- C. 880 V
- D. 8,800 V Discuss
Correct Answer: 880 V
Explanation:
V2/V1 = N2/N1
Turns ratio = N2/N1 = 8.
V2/110 = 8
V2 = 8 x 110
V2 = 880v.
Turns ratio = N2/N1 = 8.
V2/110 = 8
V2 = 8 x 110
V2 = 880v.
- 6. If a transformer has 50 turns in the primary winding and 10 turns in the secondary winding, what is the reflective resistance if the secondary load resistance is 250 Ω?
Options- A. 250 Ω
- B. 25 Ω
- C. 6,250 Ω
- D. 62,500 Ω Discuss
Correct Answer: 6,250 Ω
- 7. To step 120 V ac up to 900 V ac, the turns ratio must be
Options- A. 75
- B. 750
- C. 7.5
- D. 0.13 Discuss
Correct Answer: 7.5
- 8. A certain amplifier has 600 Ω internal resistance looking from its output. In order to provide maximum power to a 4 Ω speaker, what turns ratio must be used in the coupling transformer?
Options- A. 8
- B. 0.8
- C. 0.08
- D. 80 Discuss
Correct Answer: 0.08
- 9. The mutual inductance when k = 0.65, L1 = 2 µH, and L2 = 5 µH is
Options- A. 2 mH
- B. 2 µH
- C. 4 µH
- D. 8 µH Discuss
Correct Answer: 2 µH
- 10. The turns ratio required to match an 80 Ω source to a 320 Ω load is
Options- A. 80
- B. 20
- C. 4
- D. 2 Discuss
Correct Answer: 2
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