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# Electricity, Magnetism, and Electronics Practice Test

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By McGraw-Hill Professional
Updated on Aug 29, 2011

## Electricity, Magnetism, and Electronics Practice Test

A good score is at least 37 correct. Answers are in the back of the book. It is best to have a friend check your score the first time so that you won’t memorize the answers if you want to take the test again.

1. According to Kirchhoff’s voltage law,

(a) the sum of the voltages going around any branch in a dc circuit is equal to zero.

(b) the current in a series dc circuit is equal to the voltage divided by the power.

(c) the power in a parallel dc circuit is equal to the voltage divided by the current.

(d) the voltage in any dc circuit is equal to the power divided by the resistance.

(e) the voltage in any dc circuit is equal to the resistance squared divided by the power.

2. Suppose that an air-core loop of wire consisting of one turn carries a certain amount of dc. If the number of turns in the loop is doubled while the current remains the same, the magnetomotive force is

(a) cut to one-quarter its previous value.

(b) cut in half.

(c) unchanged.

(d) doubled.

3. A diamagnetic material

(a) has permeability of zero.

(b) has permeability of less than 1.

(c) has permeability equal to 1.

(d) has permeability of greater than 1.

(e) can have any permeability.

4. Conductance is specified in units called

(a) ohms.

(c) henrys.

(d) Siemens.

(e) coulombs.

5. Suppose that a coil carries 100 mA of dc, and then this current is reduced to 10 mA. Assume that all other factors remain the same. The intensity of the magnetic field inside and around the coil

(a) does not change.

(b) becomes 1 percent as great.

(c) becomes 10 percent as great.

(d) becomes 10 times as great.

(e) changes, but to an extent that cannot be determined unless we have more information.

6. If all other factors are held constant, the capacitance between a pair of parallel, flat, identical metal plates

(a) increases as the surface area of the plates increases.

(b) does not change as the surface area of the plates increases.

(c) decreases as the surface area of the plates increases.

(d) depends on the voltage applied to the plates.

(e) depends on the current flowing between the plates.

7. A certain ac wave has a positive peak voltage of +10.0 V and a negative peak voltage of −5.00 V. What is the peak-to-peak voltage?

(a) +5.00 V

(b) 5.00 V

(c) −5.00 V

(d) 15.0 V

(e) It cannot be calculated from this information.

8. What happens to the inductance of a coil of wire if a ferromagnetic core is placed inside it?

(a) The inductance decreases.

(b) The inductance stays the same.

(c) The inductance increases.

(d) The inductance might increase or decrease depending on the frequency.

(e) There is no way to say.

9. Which of the following certainly would not contain a solenoid?

(a) A bell ringer

(b) An electromagnet

(c) A relay

(d) An inductor

(e) A capacitor

10. An ionized gas

(b) can be a fair conductor of electricity.

(c) has too few protons in the nuclei of its atoms.

(d) has too few neutrons in the nuclei of its atoms.

(e) has too many electrons in the nuclei of its atoms.

11. The aurorae (“northern lights” or “southern lights”) are caused indirectly by

(a) the geomagnetic wind.

(c) the motions of the planets around the Sun.

(d) bombardment of the Earth’s upper atmosphere by meteors.

(e) solar flares.

12. Suppose that an air-core wire coil has an inductance of 10.0 μH at a frequency of 2.00 MHz. What is the inductance of this same coil if the frequency is doubled to 4.00 MHz?

(a) 10.0 μH

(b) 20.0 μH

(c) 5.00 μH

(d) 40.0 μH

(e) 2.50 μH

13. A certain radio wave has a frequency of 0.045 GHz. This would more likely be expressed as

(a) 45 Hz.

(b) 450 Hz.

(c) 45 kHz.

(d) 450 kHz.

(e) none of the above.

14. As the frequency of an ac voltage across a capacitor increases, a point will be reached eventually where the capacitor behaves, with respect to the ac, like

(a) a resistor.

(b) an inductor.

(c) an open circuit.

(d) a short circuit.

(e) a diode.

15. Complex impedance consists of

(a) resistance and reactance.

(b) conductance and resistance.

(c) inductance and capacitance.

(d) conductance and inductance.

(e) conductance and capacitance.

16. A resistor has a value of 220 ohms and carries 100 mA of direct current. The voltage across this resistor is

(a) 22 kV.

(b) 2.2 V.

(c) 22.0 V.

(d) 0.22 V

(e) impossible to calculate from this information.

17. A photovoltaic cell

(a) is a rechargeable electrochemical cell.

(b) is used as a variable capacitor.

(c) generates dc when visible light strikes its p-n junction.

(d) lights up when reverse-biased.

(e) is useful as a voltage regulator.

18. Magnetic flux density can be expressed in terms of

(a) lines per pole.

(b) lines per centimeter.

(c) lines per meter.

(d) lines per meter squared.

(e) lines per meter cubed.

19. In a bipolar transistor, what happens to the maximum obtainable amplification as the operating frequency becomes higher and higher?

(a) It increases.

(b) It increases up to a certain value and then levels off.

(c) It does not change.

(d) It decreases.

(e) It decreases to zero and then becomes negative.

20. Resistances in parallel

(b) add together like capacitances in series.

(c) add together like inductances in series.

(d) all draw the same amount of current no matter what their individual ohmic values.

(e) all dissipate the same amount of power no matter what their individual ohmic values.

21. Which of the following is a general difference between a pnp bipolar transistor circuit and an npn bipolar transistor circuit?

(a) The operating frequencies are different.

(b) The current-handling capabilities are different.

(c) The devices exhibit opposite types of reactance.

(d) The devices exhibit different impedances.

(e) The power-supply polarities are opposite.

22. Suppose that you read in a technical paper that two ac signals have identical frequencies and identical waveforms and that their negative peak voltages are the same as their positive peak voltages. You are also told that the signals are in phase coincidence. From this you can conclude that

(a) the peak-to-peak voltage of the composite signal is twice the peak-to-peak voltage of either signal taken alone.

(b) the peak-to-peak voltage of the composite signal is half the peak-to-peak voltage of either signal taken alone.

(c) the peak-to-peak voltage of the composite signal is 1.414 times the peak-to-peak voltage of either signal taken alone.

(d) the peak-to-peak voltage of the composite signal is 2.828 times the peak-to-peak voltage of either signal taken alone.

(e) the paper contains a mistake.

23. The width of the channel in a JFET depends on

(a) the gate voltage.

(b) the base current.

(c) the alpha cutoff.

(d) the beta.

(e) the collector current.

24. The instantaneous amplitude of an ac wave is

(a) the amplitude as measured or defined at some specific moment in time.

(b) the amplitude averaged over any exact whole number of wave cycles.

(c) equal to approximately 0.707 times the peak amplitude.

(d) equal to approximately 1.414 times the peak amplitude.

(e) constant with the passage of time.

25. In an electromagnet,

(a) the current in the coil temporarily magnetizes the core.

(b) the electrical field alternates constantly.

(c) the field strength is inversely proportional to the current.

(d) the magnetic lines of flux are all straight.

(e) there is only one pole.

26. What happens when the emitter-base ( E-B ) junction of a field-effect transistor (FET) is reverse-biased?

(a) A large current flows.

(b) The FET is optimally efficient.

(c) The reactance is zero.

(d) The device can be used as an amplifier but not as a switch.

(e) This is a meaningless question! No FET has an E-B junction.

27. Suppose that you read in a technical paper that two particular sine waves have different frequencies but are in phase coincidence. You conclude that

(a) the phase angle is 0°.

(b) the phase angle is 180°.

(c) the phase angle is +90°.

(d) the phase angle is −90°.

(e) the paper contains a mistake.

28. Five capacitors are connected in parallel. They all have capacitances of 100 pF. The total capacitance is

(a) 20 pF.

(b) 100 pF.

(c) 500 pF.

(d) dependent on the frequency.

(e) dependent on the voltage.

29. A microphone is specified as having an “impedance of 500 ohms.” The engineers mean that the microphone is designed to operate best with a circuit whose complex-number impedance is

(a) 0 + j 500.

(b) 0 − j 500.

(c) 300 + j 400.

(d) 300 − j 400.

(e) 500 + j 0.

30. Four resistances are connected in series. Three of them have values of 100 ohms; the fourth resistance is unknown. A battery of 6.00 V is connected across the series combination, producing a current of 10.0 mA through the circuit. What is the value of the unknown resistor?

(a) 300 ohms

(b) 600 ohms

(c) 900 ohms

(d) 1,200 ohms

(e) It cannot be calculated from this information.

31. Magnetic tape most likely would be found in

(a) a transistorized amplifier.

(b) a high-capacity computer data storage system.

(c) a high-fidelity compact-disc player.

(d) a computer hard drive.

(e) none of the above; magnetic tape is never used anymore.

32. Which of the following is not an asset of integrated circuits?

(a) Low power requirements

(b) Excellent reliability

(c) Substantial physical bulk

(d) Ease of maintenance

(e) Modular construction

33. The angular frequency of a certain ac wave is 450 rad/s. What is the frequency in kilohertz?

(a) 0.716 kHz

(b) 0.450 kHz

(c) 0.0716 kHz

(d) 71.6 kHz

(e) 2,830 kHz

34. In a varactor,

(a) the resistance varies with the current.

(b) the p-n junction does not conduct when forward-biased.

(c) the capacitance varies with the applied reverse voltage.

(d) the inductance depends on the reverse current.

(e) the avalanche voltage is about 0.3 V.

35. When two waves having identical frequencies are in phase opposition, they are displaced by approximately

(e) an amount that cannot be determined unless we are given more information.

36. A certain component has 50 ohms of resistance and -70 ohms of reactance. The complex-number impedance is

(a) 50 + j 70.

(b) 50 − j 70.

(c) −50+ j 70.

(d) −50− j 70.

37. Three light bulbs are connected in parallel across a 12.0-V battery. The first bulb consumes 5.00 W of power, the second bulb consumes 15.0 W, and the third bulb consumes 20.0 W. What is the current through the third bulb?

(a) 139 mA

(b) 600 mA

(c) 1.67 A

(d) 7.20 A

(e) It cannot be calculated from this information.

38. In an n -channel JFET, as the gate voltage becomes more and more negative, a point is reached eventually at which

(a) the channel conducts current as well as it possibly can.

(b) the channel does not conduct current.

(c) the amplification factor levels off.

(d) the device attains a state of saturation.

(e) the beta of the device becomes equal to 1.

39. In an ideal reverse-biased diode in which the applied dc voltage is less than the avalanche voltage,

(a) the current through the p-n junction is zero.

(b) the current through the p-n junction is high.

(c) electrons flow from the p -type material to the n -type material.

(d) electrons flow from the n -type material to the p -type material.

(e) electrons and holes flow in the same direction.

40. If you are told that wave X leads wave Y by 225°, you would do better by saying that

(a) wave X lags wave Y by 135°.

(b) wave X lags wave Y by 45°.

(c) wave X leads wave Y by 45°.

(d) wave X and wave Y are in phase opposition.

(e) wave X and wave Y are in phase coincidence.

41. Suppose that three inductors are connected in series. Suppose also that there is no mutual inductance among them and that they each exhibit a reactance of 0 + j 300 at a frequency of 500 kHz. Also imagine that all three inductors are coils made of perfectly conducting wire; that is, they all have zero resistance. What is the complex-number impedance of the series combination at 500 kHz?

(a) 0 + j 100

(b) 0 − j 100

(c) 0 + j 900

(d) 0 − j 900

42. Imagine that a dc circuit carries I amperes, has an emf source of E volts, and has a resistance of R ohms in which P watts of power are dissipated. Which of the following formulas is incorrect?

(a) P = I 2 R

(b) E = IR

(c) R = E / I

(d) P = E 2 / R

(e) I = ER

43. The rms ac input signal current to a bipolar-transistor amplifier is 10.0 μA, and the alpha cutoff of the device is 100 kHz. What is the rms ac output signal current?

(a) 10.0 mA

(b) 10.0 μA

(c) 0.100 μA

(d) 0.00100 μA

44. A simple dc circuit consists of a 12-V battery and a lamp whose resistance is 144 Ω when the battery is connected to it and the lamp is glowing. How much power is dissipated by the lamp?

(a) 83 mW

(b) 1.0 W

(c) 12 W

(d) 1.7 kW

(e) 21 kW

45. In a rectangular ac wave,

(a) the amplitude transitions occur instantaneously.

(b) the amplitude becomes more positive at a steady rate and becomes more negative instantaneously.

(c) the amplitude becomes more negative at a steady rate and becomes more positive instantaneously.

(d) the amplitude changes both positively and negatively at a steady rate.

(e) the waveform looks like the mathematical sine function.

46. A purely resistive impedance is also said to be

(a) nonconductive.

(b) noncapacitive.

(c) noninductive.

(d) nonreactive.

(e) purely imaginary.

47. The average amplitude of a pure ac sine wave is

(a) the same as the peak amplitude.

(b) approximately 0.707 times the peak amplitude.

(c) approximately 0.707 times the instantaneous amplitude.

(d) approximately 0.707 times the peak-to-peak amplitude.

(e) zero.

48. An energy transducer that converts mechanical motion into ac is

(a) an electric motor.

(b) a solenoid.

(c) an electromagnet.

(d) an electric generator.

(e) an inductor.

49. The vertical component of the geomagnetic field at any particular location is known as the

(a) flux density.

(b) flux angle.

(c) inclination.

(d) declination.

(e) right ascension.

50. Conventional current

(a) flows from minus to plus.

(b) flows from plus to minus.

(c) flows only in perfect insulators.

(d) cannot flow in an ionized gas.

(e) is measured in amperes per second.

1. a

2. d

3. b

4. d

5. c

6. a

7. d

8. c

9. e

10. b

11. e

12. a

13. e

14. d

15. a

16. c

17. c

18. d

19. d

20. b

21. e

22. a

23. a

24. a

25. a

26. e

27. e

28. c

29. e

30. a

31. b

32. c

33. c

34. c

35. c

36. b

37. c

38. b

39. a

40. a

41. c

42. e

43. e

44. b

45. a

46. d

47. e

48. d

49. c

50. b

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