# Transformers and Impedance Matching – Gibilisco MCQs in Electronics

(Last Updated On: December 8, 2017) This is the Multiple Choice Questions (MCQs) in Chapter 18: Transformers and Impedance Matching from the book Teach Yourself Electricity and Electronics, 5th edition by Stan Gibilisco. If you are looking for a reviewer in Electronics Engineering this will definitely help you before taking the Board Exam.

### Start Practice Exam Test Questions

1. In a step-up transformer:

• A. The primary impedance is greater than the secondary impedance.
• B. The secondary winding is right on top of the primary.
• C. The primary voltage is less than the secondary voltage.
• D. All of the above.

2. The capacitance between the primary and the secondary windings of a transformer can be minimized by:

• A. Placing the windings on opposite sides of a toroidal core.
• B. Winding the secondary right on top of the primary.
• C. Using the highest possible frequency.
• D. Using a center tap on the balanced winding.

3. A transformer steps a voltage down from 117 V to 6.00 V. What is its primary-to-secondary turns ratio?

• A. 1:380.
• B. 380:1.
• C. 1:19.5.
• D. 19.5:1.

4. A step-up transformer has a primary-to-secondary turns ratio of 1:5.00. If 117V RMS appears at the primary, what is the RMS voltage across the secondary?

• A. 23.4 V.
• B. 585 V.
• C. 117 V.
• D. 2.93 kV.

5. A transformer has a secondary-to-primary turns ratio of 0.167. This transformer is:

• A. A step-up unit.
• B. A step-down unit.
• C. Neither step-up nor step-down.
• D. A reversible unit.

6. Which of the following is false, concerning air cores versus ferromagnetic cores?

• A. Air concentrates the magnetic lines of flux.
• B. Air works at higher frequencies than ferromagnetic.
• C. Ferromagnetic are lossier than air.
• D. A ferromagnetic-core unit needs fewer turns of wire than an equivalent air-core unit.

7. Eddy currents cause:

• A. An increase in efficiency.
• B. An increase in coupling between windings.
• C. An increase in core loss.
• D. An increase in usable frequency range.

8. A transformer has 117 V RMS across its primary and 234 V RMS across its secondary. If this unit is reversed, assuming it can be done without damaging the windings, what will be the voltage at the output?

• A. 234 V.
• B. 468 V.
• C. 117 V.
• D. 58.5 V.

9. The shell method of transformer winding:

• A. Provides maximum coupling.
• B. Minimizes capacitance between windings.
• C. Withstands more voltage than other winding methods.
• D. Has windings far apart but along a common axis.

10. Which of these core types, in general, is best if you need a winding inductance of 1.5 H?

• A. Air core.
• B. Ferromagnetic solenoid core.
• C. Ferromagnetic toroid core.
• D. Ferromagnetic pot core.

11. An advantage of a toroid core over a solenoid core is:

• A. The toroid works at higher frequencies.
• B. The toroid confines the magnetic flux.
• C. The toroid can work for dc as well as for ac.
• D. It’s easier to wind the turns on a toroid.

12. High voltage is used in long-distance power transmission because:

• A. It is easier to regulate than low voltage.
• B. The I2R losses are lower.
• C. The electromagnetic fields are stronger.
• D. Smaller transformers can be used.

13. In a household circuit, the 234-V power has:

• A. One phase.
• B. Two phases.
• C. Three phases.
• D. Four phases.

14. In a transformer, a center tap would probably be found in:

• A. The primary winding.
• B. The secondary winding.
• C. The unbalanced winding.
• D. The balanced winding.

15. An autotransformer:

• A. Works automatically.
• B. Has a center-tapped secondary.
• C. Has one tapped winding.
• D. Is useful only for impedance matching.

16. A transformer has a primary-to-secondary turns ratio of 2.00:1. The input impedance is 300 Ω resistive. What is the output impedance?

• A. 75 Ω
• B. 150 Ω
• C. 600 Ω
• D. 1200 Ω

17. A resistive input impedance of 50 Ω must be matched to a resistive output impedance of 450 Ω. The primary-to-secondary turns ratio of the transformer must be:

• A. 9.00:1.
• B. 3.00:1.
• C. 1:3.00.
• D. 1:9.00.

18. A quarter-wave matching section has a characteristic impedance of 75.0 Ω. The input impedance is 50.0 Ω resistive. What is the resistive output impedance?

• A. 150 Ω
• B. 125 Ω
• C. 100 Ω
• D. 113 Ω

19. A resistive impedance of 75 Ω must be matched to a resistive impedance of 300 Ω. A quarter-wave section would need:

• A. Zo = 188 Ω
• B. Zo = 150 Ω
• C. Zo = 225 Ω
• D. Zo = 375 Ω

20. If there is reactance at the output of an impedance transformer:

• A. The circuit will not work.
• B. There will be an impedance mismatch, no matter what the turns ratio of the transformer.
• C. A center tap must be used at the secondary.
• D. The turns ratio must be changed to obtain a match.

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