Monday, October 20, 2014

How Diodes Are Used - Gibilisco MCQs in Electronics

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Multiple choice questions in How Diodes Are Used

This is the Multiple Choice Questions (MCQs) in Chapter 20: How Diodes Are Used 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.

Begin the Test

1. When a diode is forward-biased, the anode:

  • A. Is negative relative to the cathode.
  • B. Is positive relative to the cathode.
  • C. Is at the same voltage as the cathode.
  • D. Alternates between positive and negative relative to the cathode.

2. If ac is applied to a diode, and the peak ac voltage never exceeds the avalanche voltage, then the output is:

  • A. Ac with half the frequency of the input.
  • B. Ac with the same frequency as the input.
  • C. Ac with twice the frequency of the input.
  • D. None of the above.

3. A crystal set:

  • A. Can be used to transmit radio signals.
  • B. Requires a battery with long life.
  • C. Requires no battery.
  • D. Is useful for rectifying 60-Hz ac.

4. A diode detector:

  • A. Is used in power supplies.
  • B. Is employed in some radio receivers.
  • C. Is used commonly in high-power radio transmitters.
  • D. Changes dc into ac.

5. If the output wave in a circuit has the same shape as the input wave, then:

  • A. The circuit is linear.
  • B. The circuit is said to be detecting.
  • C. The circuit is a mixer.
  • D. The circuit is a rectifier.

6. The two input frequencies of a mixer circuit are 3.522 MHz and 3.977 MHz. Which of the following frequencies might be used at the output?

  • A. 455 kHz.
  • B. 886 kHz.
  • C. 14.00 MHz.
  • D. 1.129 MHz.

7. A time-domain display might be found in:

  • A. An ammeter.
  • B. A spectrum analyzer.
  • C. A digital voltmeter.
  • D. An oscilloscope.

8. Zener voltage is also known as:

  • A. Forward breakover voltage.
  • B. Peak forward voltage.
  • C. Avalanche voltage.
  • D. Reverse bias.

9. The forward breakover voltage of a silicon diode is:

  • A. About 0.3 V.
  • B. About 0.6 V.
  • C. About 1.0 V.
  • D. Dependent on the method of manufacture.

10. A diode audio limiter circuit:

  • A. Is useful for voltage regulation.
  • B. Always uses Zener diodes.
  • C. Rectifies the audio to reduce distortion.
  • D. Can cause objectionable signal distortion.

11. The capacitance of a varactor varies with:

  • A. Forward voltage.
  • B. Reverse voltage.
  • C. Avalanche voltage.
  • D. Forward breakover voltage.

12. The purpose of the I layer in a PIN diode is to:

  • A. Minimize the diode capacitance.
  • B. Optimize the avalanche voltage.
  • C. Reduce the forward breakover voltage.
  • D. Increase the current through the diode.

13. Which of these diode types might be found in the oscillator circuit of a

microwave radio transmitter?

  • A. A rectifier diode.
  • B. A cat whisker.
  • C. An IMPATT diode.
  • D. None of the above.

14. A Gunnplexer can be used as a:

  • A. Communications device.
  • B. Radio detector.
  • C. Rectifier.
  • D. Signal mixer.

15. The most likely place you would find an LED would be:

  • A. In a rectifier circuit.
  • B. In a mixer circuit.
  • C. In a digital frequency display.
  • D. In an oscillator circuit.

16. Coherent radiation is produced by a:

  • A. Gunn diode.
  • B. Varactor diode.
  • C. Rectifier diode.
  • D. Laser diode.

17. You want a circuit to be stable with a variety of amplifier impedance

conditions. You might consider a coupler using:

  • A. A Gunn diode.
  • B. An optoisolator.
  • C. A photovoltaic cell.
  • D. A laser diode.

18. The power from a solar panel depends on all of the following except:

  • A. The operating frequency of the panel.
  • B. The total surface area of the panel.
  • C. The number of cells in the panel.
  • D. The intensity of the light.

19. Emission of energy in an IRED is caused by:

  • A. High-frequency radio waves.
  • B. Rectification.
  • C. Electron energy-level changes.
  • D. None of the above.

20. A photodiode, when not used as a photovoltaic cell, has:

  • A. Reverse bias.
  • B. No bias.
  • C. Forward bias.
  • D. Negative resistance.

Published by: Froyd Wess17:48

Introduction to Semiconductors - Gibilisco MCQs in Electronics - Answers

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Answers key in Introduction to Semiconductors MCQs

Below are the answers key for the Multiple Choice Questions (MCQs) in Chapter 19: Introduction to Semiconductors from the book Teach Yourself Electricity and Electronics, 5th edition by Stan Gibilisco.

1. Variable conductive properties of some materials.

2. Ability to withstand high voltages.

3. Silicon.

4. Compound.

5. It is expensive to produce.

6. Photocells.

7. Germanium.

8. Is susceptible to damage by static.

9. Give a semiconductor material certain properties.

10. Adding a donor impurity.

11. The substance has an electron surplus.

12. Minority carriers.

13. Plus to minus.

14. Reverse biased.

15. Charge carriers are passed from atom to atom.

16. A charge of +1 unit.

17. The frequency.

18. The junction will conduct current.

19. Voltage regulator.

20. The reverse current.


Published by: Froyd Wess17:37

Introduction to Semiconductors - Gibilisco MCQs in Electronics

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Multiple choice questions in Introduction to Semiconductors

This is the Multiple Choice Questions (MCQs) in Chapter 19: Introduction to Semiconductors 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.

Begin the Test

1. The term “semiconductor” arises from:

  • A. Resistor-like properties of metal oxides.
  • B. Variable conductive properties of some materials.
  • C. The fact that there’s nothing better to call silicon.
  • D. Insulating properties of silicon and GaAs.

2. Which of the following is not an advantage of semiconductor devices over vacuum tubes?

  • A. Smaller size.
  • B. Lower working voltage.
  • C. Lighter weight.
  • D. Ability to withstand high voltages.

3. The most common semiconductor among the following substances is:

  • A. Germanium.
  • B. Galena.
  • C. Silicon.
  • D. Copper.

4. GaAs is a(n):

  • A. Compound.
  • B. Element.
  • C. Conductor.
  • D. Gas.

5. A disadvantage of gallium-arsenide devices is that:

  • A. The charge carriers move fast.
  • B. The material does not react to ionizing radiation.
  • C. It is expensive to produce.
  • D. It must be used at high frequencies.

6. Selenium works especially well in:

  • A. Photocells.
  • B. High-frequency detectors.
  • C. Radio-frequency power amplifiers.
  • D. Voltage regulators.

7. Of the following, which material allows the lowest forward voltage drop in a diode?

  • A. Selenium.
  • B. Silicon.
  • C. Copper.
  • D. Germanium.

8. A CMOS integrated circuit:

  • A. Can only work at low frequencies.
  • B. Is susceptible to damage by static.
  • C. Requires considerable power to function.
  • D. Needs very high voltage.

9. The purpose of doping is to:

  • A. Make the charge carriers move faster.
  • B. Cause holes to flow.
  • C. Give a semiconductor material certain properties.
  • D. Protect devices from damage in case of transients.

10. A semiconductor material is made into N type by:

  • A. Adding an acceptor impurity.
  • B. Adding a donor impurity.
  • C. Injecting electrons.
  • D. Taking electrons away.

11. Which of the following does not result from adding an acceptor impurity?

  • A. The material becomes P type.
  • B. Current flows mainly in the form of holes.
  • C. Most of the carriers have positive electric charge.
  • D. The substance has an electron surplus.

12. In a P-type material, electrons are:

  • A. Majority carriers.
  • B. Minority carriers.
  • C. Positively charged.
  • D. Entirely absent.

13. Holes flow from:

  • A. Minus to plus.
  • B. Plus to minus.
  • C. P-type to N-type material.
  • D. N-type to P-type material.

14. When a P-N junction does not conduct, it is:

  • A. Reverse biased.
  • B. Forward biased.
  • C. Biased past the breaker voltage.
  • D. In a state of avalanche effect.

15. Holes flow the opposite way from electrons because:

  • A. Charge carriers flow continuously.
  • B. Charge carriers are passed from atom to atom.
  • C. They have the same polarity.
  • D. No! Holes flow in the same direction as electrons.

16. If an electron has a charge of -1 unit, a hole has:

  • A. A charge of -1 unit.
  • B. No charge.
  • C. A charge of +1 unit.
  • D. A charge that depends on the semiconductor type.

17. When a P-N junction is reverse-biased, the capacitance depends on all of the following except:

  • A. The frequency.
  • B. The width of the depletion region.
  • C. The cross-sectional area of the junction.
  • D. The type of semiconductor material.

18. If the reverse bias exceeds the avalanche voltage in a P-N junction:

  • A. The junction will be destroyed.
  • B. The junction will insulate; no current will flow.
  • C. The junction will conduct current.
  • D. The capacitance will become extremely high.

19. Avalanche voltage is routinely exceeded when a P-N junction acts as:

  • A. Current rectifier.
  • B. Variable resistor.
  • C. Variable capacitor.
  • D. Voltage regulator.

20. An unimportant factor concerning the frequency at which a P-N junction will work effectively is:

  • A. The type of semiconductor material.
  • B. The cross-sectional area of the junction.
  • C. The reverse current.
  • D. The capacitance with reverse bias.

Published by: Froyd Wess17:35

Teach Yourself Electricity and Electronics Examination Part 2 - Answers

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Answers key in Teach Yourself Electricity and Electronics Examination Part 2 MCQs

Below are the answers key for the Part 2 Examination Test that includes the the succeeding 10 Chapters of the book Teach Yourself Electricity and Electronics, 5th edition by Stan Gibilisco.

1. 100 - j200.

2. Vary, depending on the extent and phase of mutual coupling.

3. Leading wave B by 90 degrees.

4. 21.2 V.

5. 400 pF.

6. 26.4 V rms.

7. 90 degrees.

8.  Meaningless; true power is dissipated, not transmitted.

9. Simply add up.

10. 72 degrees.

11. −189 Ω

12. 50.0 Ω

13. 41 Ω

14. 471 Ω

15. 1/2 cycle.

16. Power factor.

17. 80 + j20.

18. 1.64 mH.

19. Electrolytic.

20. Is essentially self-shielding.

21. Is equal to output power divided by driving power.

22. A measure of the ease with which a circuit passes ac.

23. Z2= RX / (R2 + X2).

24. They provide a way to represent what happens in resistance-reactance circuits.

25. The frequency (within reason).

26. Zero and positive-going.

27. Varying the net core permeability.

28. True power to VA power.

29. Zo = 100 Ω

30. 40 Ω resistance and 30 Ω inductive reactance.

31. The current leads the voltage by a few degrees.

32. The primary voltage is greater than the secondary voltage.

33. 3.49 MHz.

34. Just one frequency.

35. Negative imaginary.

36. Leads the original wave by 90 degrees of phase.

37. Vector difference of VA and reactive power.

38. 22 μF.

39. The current in the line.

40. Find the net conductance and susceptance, then convert to resistance and reactance, and add these to get R + jX.

41. XL = 60 Ω and R = 25 Ω

42. 180 degrees.

43. −37 degrees.

44. 200 +  j100.

45. Depends on the construction of the line.

46. 50 MHz.

47. Not determinable from the data given.

48. Has increasing capacitance as temperature goes down.

49. 100 μH.

50. 0.531 μH.


Published by: Froyd Wess17:30

Sunday, October 19, 2014

Teach Yourself Electricity and Electronics Examination Part 2

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Multiple choice questions in Teach Yourself Electricity and Electronics Examination Part 2

This is the Part 2 Examination Test (Alternating Current) that includes the succeeding 10 Chapters of 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.

Topics Included in the Test from Chapter 9 to Chapter 18

Part 2: Alternating Current
Chapter 10: MCQs in Inductance
Chapter 12: MCQs in Phase

Begin the Test

1. A series circuit has a resistance of 100 Ω and a capacitive reactance of -200 Ω. The complex impedance is:

  • A. -200 + j100.
  • B. 100 + j200.
  • C. 200 - j100.
  • D. 200 + j100.
  • E. 100 - j200.

2. Mutual inductance causes the net value of a set of coils to:

  • A. Cancel out, resulting in zero inductance.
  • B. Be greater than what it would be with no mutual coupling.
  • C. Be less than what it would be with no mutual coupling.
  • D. Double.
  • E. Vary, depending on the extent and phase of mutual coupling.

NOTE: For questions 3 see Fig. Test 2-1

Gibilisco MCQs image for test2 Q3

3. Refer to Fig. TEST 2-1. Wave A is:

  • A. Leading wave B by 90 degrees.
  • B. Lagging wave B by 90 degrees.
  • C. Leading wave B by 180 degrees.
  • D. Lagging wave B by 135 degrees.
  • E. Lagging wave B by 45 degrees.

4. A sine wave has a peak value of 30.0 V. Its rms value is:

  • A. 21.2 V.
  • B. 30.0 V.
  • C. 42.4 V.
  • D. 60.0 V.
  • E. 90.0 V.

5. Four capacitors are connected in parallel. Their values are 100 pF each. The net capacitance is:

  • A. 25 pF.
  • B. 50 pF.
  • C. 100 pF.
  • D. 200 pF.
  • E. 400 pF.

6. A transformer has a primary-to-secondary turns ratio of exactly 8.88:1. The input voltage is 234 V rms. The output voltage is:

  • A. 2.08 kV rms.
  • B. 18.5 kV rms.
  • C. 2.97 V rms.
  • D. 26.4 V rms.
  • E. 20.8 V rms.

7. In a series RL circuit, as the resistance becomes small compared with the reactance, the angle of lag approaches:

  • A. 0 degrees.
  • B. 45 degrees.
  • C. 90 degrees.
  • D. 180 degrees.
  • E. 360 degrees.

8. A transmission line carries 3.50 A of ac current and 150 V ac. The true power in the line is:

  • A. 525 W.
  • B. 42.9 W.
  • C. 1.84 W.
  • D. Meaningless; true power is dissipated, not transmitted.
  • E. Variable, depending on standing wave effects.

9. In a parallel configuration, susceptances:

  • A. Simply add up.
  • B. Add like capacitances in series.
  • C. Add like inductances in parallel.
  • D. Must be changed to reactances before you can work with them.
  • E. Cancel out.

10. A wave has a frequency of 200 kHz. How many degrees of phase change occur in a microsecond (a millionth of a second)?

  • A. 180 degrees.
  • B. 144 degrees.
  • C. 120 degrees.
  • D. 90 degrees.
  • E. 72 degrees.

11. At a frequency of 2.55 MHz, a 330-pF capacitor has a reactance of:

  • A. −5.28 Ω
  • B. −0.00528 Ω
  • C. −189 Ω
  • D. −18.9k Ω
  • E. −0.000189 Ω

12. A transformer has a step-up turns ratio of 1:3.16. The output impedance is 499Ω purely resistive. The input impedance is:

  • A. 50.0 Ω
  • B. 158 Ω
  • C. 1.58k Ω
  • D. 4.98k Ω
  • E. Not determinable from the data given.

13. A complex impedance is represented by 34 − j23. The absolute-value impedance is:

  • A. 34 Ω
  • B. 11 Ω
  • C. -23 Ω
  • D. 41 Ω
  • E. 57 Ω

14. A coil has an inductance of 750 μH. The inductive reactance at 100 kHz is:

  • A. 75.0 Ω
  • B. 75.0 k Ω
  • C. 471 Ω
  • D. 47.1 k Ω
  • E. 212 Ω

15. Two waves are 180 degrees out of phase. This is a difference of:

  • A. 1/8 cycle.
  • B. 1/4 cycle.
  • C. 1/2 cycle.
  • D. A full cycle.
  • E. Two full cycles.

16. If R denotes resistance and Z denotes absolute-value impedance, then R/Z is the:

  • A. True power.
  • B. Imaginary power.
  • C. Apparent power.
  • D. Absolute-value power.
  • E. Power factor.

17. Two complex impedances are in series. One is 30 + j50 and the other is 50 − j30. The net impedance is:

  • A. 80 + j80.
  • B. 20 + j20.
  • C. 20 - j20.
  • D. –20 + j20.
  • E. 80 + j20.

18. Two inductors, having values of 140 μH and 1.50 mH, are connected in series. The net inductance is:

  • A. 141.5 μH.
  • B. 1.64 μH.
  • C. 0.1415 mH.
  • D. 1.64 mH.
  • E. 0.164 mH.

19. Which of the following types of capacitor is polarized?

  • A. Mica.
  • B. Paper.
  • C. Electrolytic.
  • D. Air variable.
  • E. Ceramic.

20. A toroidal-core coil:

  • A. Has lower inductance than an air-core coil with the same number of turns.
  • B. Is essentially self-shielding.
  • C. Works well as a loopstick antenna.
  • D. Is ideal as a transmission-line transformer.
  • E. Cannot be used at frequencies below about 10 MHz.

21. The efficiency of a generator:

  • A. Depends on the driving power source.
  • B. Is equal to output power divided by driving power.
  • C. Depends on the nature of the load.
  • D. Is equal to driving voltage divided by output voltage.
  • E. Is equal to driving current divided by output current.

22. Admittance is:

  • A. The reciprocal of reactance.
  • B. The reciprocal of resistance.
  • C. A measure of the opposition a circuit offers to ac.
  • D. A measure of the ease with which a circuit passes ac.
  • E. Another expression for absolute-value impedance.

23. The absolute-value impedance Z of a parallel RLC circuit, where R is the resistance and X is the net reactance, is found according to the formula:

  • A. Z = R + X.
  • B. Z2 = R2 + X2.
  • C. Z2= RX / (R2 + X2).
  • D. Z = 1/(R2 + X2).
  • E. Z = R2X2/(R + X).

24. Complex numbers are used to represent impedance because:

  • A. Reactance cannot store power.
  • B. Reactance isn’t a real physical thing.
  • C. They provide a way to represent what happens in resistance-reactance circuits.
  • D. Engineers like to work with sophisticated mathematics.
  • E. No! Complex numbers aren’t used to represent impedance.

25. Which of the following does not affect the capacitance of a capacitor?

  • A. The mutual surface area of the plates.
  • B. The dielectric constant of the material between the plates (within reason).
  • C. The spacing between the plates (within reason).
  • D. The amount of overlap between plates.
  • E. The frequency (within reason).

26. The zero-degree phase point in an ac sine wave is usually considered to be the instant at which the amplitude is:

  • A. Zero and negative-going.
  • B. At its negative peak.
  • C. Zero and positive-going.
  • D. At its positive peak.
  • E. Any value; it doesn’t matter.

27. The inductance of a coil can be continuously varied by:

  • A. Varying the frequency.
  • B. Varying the net core permeability.
  • C. Varying the current in the coil.
  • D. Varying the wavelength.
  • E. Varying the voltage across the coil.

28. Power factor is defined as the ratio of:

  • A. True power to VA power.
  • B. True power to imaginary power.
  • C. Imaginary power to VA power.
  • D. Imaginary power to true power.
  • E. VA power to true power.

29. A 50 Ω feed line needs to be matched to an antenna with a purely resistive impedance of 200 Ω A quarter-wave matching section should have:

  • A. Zo = 150 Ω
  • B. Zo = 250 Ω
  • C. Zo = 125 Ω
  • D. Zo = 133 Ω
  • E. Zo = 100 Ω

30. The vector 40 + j30 represents:

  • A. 40 Ω resistance and 30 μH inductance.
  • B. 40 uH inductance and 30 Ω resistance.
  • C. 40 Ω resistance and 30 Ω inductive reactance.
  • D. 40 Ω inductive reactance and 30 Ω resistance.
  • E. 40 uH inductive reactance and 30 Ω resistance.

31. In a series RC circuit, where, R = 300 Ω and XC = −30 Ω:

  • A. The current leads the voltage by a few degrees.
  • B. The current leads the voltage by almost 90 degrees.
  • C. The voltage leads the current by a few degrees.
  • D. The voltage leads the current by almost 90 degrees.
  • E. The voltage leads the current by 90 degrees.

32. In a step-down transformer:

  • A. The primary voltage is greater than the secondary voltage.
  • B. The primary impedance is less than the secondary impedance.
  • C. The secondary voltage is greater than the primary voltage.
  • D. The output frequency is higher than the input frequency.
  • E. The output frequency is lower than the input frequency.

33. A capacitor of 470 pF is in parallel with an inductor of 4.44 μH. What is the resonant frequency?

  • A. 3.49 MHz.
  • B. 3.49 kHz.
  • C. 13.0 MHz.
  • D. 13.0 GHz.
  • E. Not determinable from the data given.

34. A sine wave contains energy at:

  • A. Just one frequency.
  • B. A frequency and its even harmonics.
  • C. A frequency and its odd harmonics.
  • D. A frequency and all its harmonics.
  • E. A frequency and its second harmonic only.

35. Inductive susceptance is:

  • A. The reciprocal of inductance.
  • B. Negative imaginary.
  • C. Equal to capacitive reactance.
  • D. The reciprocal of capacitive susceptance.
  • E. A measure of the opposition a coil offers to ac.

36. The rate of change (derivative) of a sine wave is itself a wave that:

  • A. Is in phase with the original wave.
  • B. Is 180 degrees out of phase with the original wave.
  • C. Leads the original wave by 45 degrees of phase.
  • D. Lags the original wave by 90 degrees of phase.
  • E. Leads the original wave by 90 degrees of phase.

37. True power is equal to:

  • A. VA power plus imaginary power.
  • B. Imaginary power minus VA power.
  • C. Vector difference of VA and reactive power.
  • D. VA power; the two are the same thing.
  • E. 0.707 times the VA power.

38. Three capacitors are connected in series. Their values are 47 μF, 68 μF, and 100 μF. The total capacitance is:

  • A. 215 μF.
  • B. Between 68 μF and 100 μF.
  • C. Between 47 μF and 68 μF.
  • D. 22 μF.
  • E. Not determinable from the data given.

39. The reactance of a section of transmission line depends on all of the following except:

  • A. The velocity factor of the line.
  • B. The length of the section.
  • C. The current in the line.
  • D. The frequency.
  • E. The wavelength.

40. When confronted with a parallel RLC circuit and you need to find the complex impedance:

  • A. Just add the resistance and reactance to get R + jX.
  • B. Find the net conductance and susceptance, then convert to resistance and reactance, and add these to get R + jX.
  • C. Find the net conductance and susceptance, and just add these together to get R + jX.
  • D. Rearrange the components so they’re in series, and find the complex impedance of that circuit.
  • E. Subtract reactance from resistance to get R jX.

NOTE: For questions 41 see Fig. Test 2-2

Gibilisco MCQs image for test2 Q41

41. The illustration in Fig. Test 2-2 shows a vector R + jX representing:

  • A. XC = 60 Ω and R = 25 Ω
  • B. XL = 60 Ω and R = 25 Ω
  • C. XL = 60 μH and R = 25 Ω
  • D. C = 60 μF and R = 25 Ω
  • E. L = 60 μH and R = 25 Ω

42. If two sine waves have the same frequency and the same amplitude, but they cancel out, the phase difference is:

  • A. 45 degrees.
  • B. 90 degrees.
  • C. 180 degrees.
  • D. 270 degrees.
  • E. 360 degrees.

43. A series circuit has a resistance of 50 Ω and a capacitive reactance of −37 Ω. The phase angle is:

  • A. 37 degrees.
  • B. 53 degrees.
  • C. −37 degrees.
  • D. −53 degrees.
  • E. Not determinable from the data given.

44. A 200 Ω resistor is in series with a coil and capacitor; XL = 200 Ω and XC = −100 Ω. The complex impedance is:

  • A. 200 − j100.
  • B. 200 − j200.
  • C. 200 +  j100.
  • D. 200 + j200.
  • E. Not determinable from the data given.

45. The characteristic impedance of a transmission line:

  • A. Is negative imaginary.
  • B. Is positive imaginary.
  • C. Depends on the frequency.
  • D. Depends on the construction of the line.
  • E. Depends on the length of the line.

46. The period of a wave is 2 X 10−8 second. The frequency is:

  • A. 2 X 108 Hz.
  • B. 20 MHz.
  • C. 50 kHz.
  • D. 50 MHz.
  • E. 500 MHz.

47. A series circuit has a resistance of 600 Ω and a capacitance of 220 pF. The phase angle is:

  • A. −20 degrees.
  • B. 20 degrees.
  • C. −70 degrees.
  • D. 70 degrees.
  • E. Not determinable from the data given.

48. A capacitor with a negative temperature coefficient:

  • A. Works less well as the temperature increases.
  • B. Works better as the temperature increases.
  • C. Heats up as its value is made larger.
  • D. Cools down as its value is made larger.
  • E. Has increasing capacitance as temperature goes down.

49. Three coils are connected in parallel. Each has an inductance of 300μH. There is no mutual inductance. The net inductance is:

  • A. 100 μH.
  • B. 300 μH.
  • C. 900 μH.
  • D. 17.3 μH.
  • E. 173 μH.

50. An inductor shows 100 Ω of reactance at 30.0 MHz. What is its inductance?

  • A. 0.531 μH.
  • B. 18.8 mH.
  • C. 531 μH.
  • D. 18.8 μH.
  • E. It can’t be found from the data given.

Published by: Froyd Wess16:45

Transformers and Impedance Matching - Gibilisco MCQs in Electronics - Answers

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Answers key in Transformers and Impedance Matching MCQs

Below are the answers key for 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.

1. The primary voltage is less than the secondary voltage.

2. Placing the windings on opposite sides of a toroidal core.

3. 19.5:1.

4. 19.5:1.

5. A step-down unit.

6. Air concentrates the magnetic lines of flux.

7. An increase in core loss.

8. 58.5 V.

9. Provides maximum coupling.

10. Ferromagnetic pot core.

11. The toroid confines the magnetic flux.

12. The I2R losses are lower.

13. Three phases.

14. The balanced winding.

15. Has one tapped winding.

16. 75 Ω

17. 1:3.00.

18. 113 Ω

19. Zo = 150 Ω

20. There will be an impedance mismatch, no matter what the turns ratio of the transformer.


Published by: Froyd Wess16:27

Transformers and Impedance Matching - Gibilisco MCQs in Electronics

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Multiple choice questions in Transformers and  Impedance Matching

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.

Begin the Test

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.

Published by: Froyd Wess16:25