Gibilisco: MCQ in Transformers and Impedance Matching | ECE Board Exam

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.

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⇐ Gibilisco: MCQ in Power and Resonance in AC circuits | ECE Board Exam

Choose the letter of the best answer in each 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 glossier 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.

Topics Included in the Test from Chapter 9 to Chapter 18

Complete List of Multiple Choice Questions from this Book

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