Test: Part 3
DO NOT REFER TO THE TEXT WHEN TAKING THIS TEST. A GOOD SCORE IS AT LEAST 37 CORRECT. Answers are in the back of the book. It’s best to have a friend check your score the first time, so you won’t memorize the answers if you want to take the test again.
1. When you design a power supply that uses rectifier diodes, you must make sure that each diode can handle
(a) at least the expected average DC forward current.
(b) at least half again the expected average DC forward current.
(c) no more than 60 Hz.
(d) at least 100 V RMS.
(e) transients caused by lightning striking a nearby power line.
2. A crystal set radio receiver comprises an antenna, a detector, a headset shunted by a capacitor, and
(a) an LC circuit.
(b) an amplifier.
(c) an oscillator.
(d) a mixer.
(e) all of the above
3. If you want current to flow between the source and drain of an N-channel JFET for the entire input cycle, you must make sure that
(a) the gate-source junction remains reverse-biased, but at a voltage that never exceeds the pinchoff value during any part of the cycle.
(b) the gate-source junction remains forward-biased, but at a voltage that never exceeds the pinchoff value during any part of the cycle.
(c) the gate-source junction remains reverse-biased, but at a voltage that never falls below the pinchoff value during any part of the cycle.
(d) the gate-source junction remains forward-biased, but at a voltage that never falls below the pinchoff value during any part of the cycle.
(e) the gate-source junction remains zero-biased.
4. As you increase the negative DC gate voltage to a P-channel JFET while holding the negative DC drain voltage constant, what happens to the drain current, assuming that you apply no input signal?
(a) The drain current rises and eventually levels off when the gate-drain junction approaches a state of saturation.
(b) The drain current decreases because the channel narrows, reducing its conductance.
(c) The drain current increases because the source current increases, increasing the effective conductance of the channel.
(d) The drain current remains the same because the channel width remains constant.
(e) The drain current decreases because current bleeds off into the gate from the channel.
5. In the scenario of Question 4, suppose that you keep increasing the negative DC gate voltage while leaving the negative DC drain voltage constant. What will happen to the drain current in the absence of an input signal?
(a) The drain current will keep going down and approach zero because more and more of the channel current will bleed off through the gate.
(b) The drain current will remain constant until, at a certain point, the extreme negative gate voltage will destroy the device.
(c) The drain current will increase as the channel conductance improves, all the way up to the point at which the extreme negative gate voltage destroys the device.
(d) The channel current will drop to zero and then reverse direction.
(e) The drain current will attain its maximum value for the particular DC drain voltage that you apply.
6. If you increase by tenfold the power dissipated by a load that has no reactance, you get
(a) 3 dB gain.
(b) 6 dB gain.
(c) 10 dB gain.
(d) 20 dB gain.
(e) 100 dB gain.
7. If you increase by tenfold the voltage across a load that has no reactance, you get
(a) 3 dB gain.
(b) 6 dB gain.
(c) 10 dB gain.
(d) 20 dB gain.
(e) 100 dB gain.
8. In a depletion-mode JFET, DC gate bias of the appropriate polarity
(a) keeps the input signal from leaking through to the source.
(b) prevents destruction of the device by electrostatic discharge.
(c) keeps the device from oscillating.
(d) constricts the channel between the source and drain.
(e) forms a channel between the source and drain.
9. If you double the RMS current through a load with a purely resistive impedance, you get a gain of
(a) 3 dB.
(b) 4 dB.
(c) 6 dB.
(d) 8 dB.
(e) 12 dB.
10. How does the phase of the AC output signal compare with the phase of the AC input signal in a class-A, common-emitter, bipolar-transistor amplifier?
(a) The output and input waves coincide in phase.
(b) The output wave leads the input wave by 90°.
(c) The output wave lags the input wave by 90°.
(d) The output and input waves oppose each other in phase.
(e) In an NPN device, the output wave leads the input wave by 90°; in a PNP device, the output wave lags the input wave by 90°.
11. Figure Test 3-1 shows the situation inside a semiconductor diode under certain conditions. The small black dots represent majority carriers on either side of the P-N junction. The presence of a depletion region suggests
Test 3-1 Illustration for Part 3 Test Questions 11 and 12.
(a) forward bias.
(b) reverse bias.
(c) zero bias.
(d) that the diode is intended for switching.
(e) that the diode is intended for rectification.
12. In the scenario of Fig. Test 3-1, the particles moving toward point X are
(a) protons.
(b) neutrons.
(c) electrons.
(d) positrons.
(e) holes.
13. A PIN diode works best as a
(a) rectifier.
(b) detector.
(c) mixer.
(d) frequency multiplier.
(e) high-speed switch.
14. Figure Test 3-2 shows a circuit that’s intended for the output of an AC-to-DC power supply. The resistor
Test 3-2 Illustration for Part 3 Test Question 14.
(a) limits the output voltage.
(b) limits the current that the Zener diode must handle.
(c) maximizes the output voltage.
(d) maximizes the current that the supply can deliver.
(e) keeps the output power under control.
15. A class-B bipolar-transistor power amplifier operates with an efficiency of 50%. We measure the RMS output power as 70 W across a load devoid of reactance. What’s the DC collector input power?
(a) 35 W
(b) 49 W
(c) 99 W
(d) 140 W
(e) We need more information to figure it out.
16. A class-C power amplifier using a 250-TH vacuum tube has a plate power input of 300 W and an RF power output of 225 W into a 50-ohm, reactance-free load at 3.550 MHz. (Have you ever seen one of things? It’s a relic! Google on “250-TH vacuum tube” as a phrase.) What’s the efficiency of this amplifier?
(a) 66%
(b) 75%
(c) 80%
(d) 88%
(e) 92%
17. In an IC, component density correlates directly with
(a) operating speed.
(b) power output.
(c) voltage rating.
(d) current drain.
(e) All of the above
18. If you input signals at 6.0 MHz and 2.5 MHz to a mixer, at which of the following frequencies should you not expect to get any output?
(a) 8.5 MHz
(b) 3.5 MHz
(c) 6.0 MHz
(d) 15.0 MHz
(e) 2.5 MHz
19. What’s a major advantage of frequency-shift keying (FSK) over simple on/off keying such as Morse code?
(a) Narrower bandwidth
(b) Higher speed
(d) Improved frequency stability
(e) Reduced harmonic emission
20. In which of the following systems could you use a vacuum tube instead of a transistor?
(a) Hi-fi audio power amplifier
(b) Radio-frequency (RF) oscillator
(c) RF power amplifier
(d) Weak-signal RF amplifier
(e) All of the above
21. Figure Test 3-3 is a diagram of a power supply designed to produce high-voltage DC. It lacks an essential circuit. What is it, and what should it do?
Test 3-3 Illustration for Part 3 Test Questions 21 through 24.
(a) A filter to get pure DC at the output
(b) A capacitor to regulate the output voltage
(c) A resistor to limit the output current
(d) A diode to double the ripple frequency
(e) A coil to stabilize the output power
22. What’s the purpose of the components marked X in Fig. Test 3-3?
(a) Stabilize the input voltage
(b) Limit the power that the device consumes
(c) Keep the input terminals from shorting to ground
(d) Ensure that the input is a pure AC sine wave
(e) None of the above
23. In Fig. Test 3-3, what’s the component represented by the symbol marked Y?
(a) A current limiter
(b) A rectifier
(c) An AC line filter
(d) An incandescent lamp
(e) A fuse
24. In Fig. Test 3-3, what’s the component represented by the symbol marked Z?
(a) An isolation transformer
(b) A step-up transformer
(c) A wave-smoothing coil
(d) A ripple filter
(e) A transient suppressor
25. Figure Test 3-4 shows the schematic symbol for
Test 3-4 Illustration for Part 3 Test Questions 25 and 26.
(a) an NPN bipolar transistor.
(b) a PNP bipolar transistor.
(c) an N-channel JFET.
(d) a P-channel JFET.
(e) an enhancement-mode MOSFET.
26. In Fig. Test 3-4, what’s the electrode represented by the line with the arrow?
(a) The gate
(b) The emitter
(c) The source
(d) The collector
(e) The base
27. Which of the following components will you find in an optoisolator?
(a) Photodiode
(b) Bipolar transistor
(c) Field-effect transistor (FET)
(d) Capacitor
(e) Digital integrated circuit (IC)
28. You bias a JFET beyond pinchoff (under no-input-signal conditions) for use as an RF power amplifier. It takes a fairly strong input signal to produce any output. Even then, channel current flows for less than half the cycle. You have a
(a) class-A amplifier.
(b) class-AB1 amplifier.
(c) class-AB2 amplifier.
(d) class-B amplifier.
(e) class-C amplifier.
29. Imagine that over a small range, an increase in the voltage across a component causes the current to decrease. This is an example of
(a) negative resistance.
(b) parasitic conduction.
(c) current-reversal effect.
(d) avalanche effect.
(e) None of the above, because such a situation can never occur.
30. Figure Test 3-5 shows how the collector current varies as a function of the base current for a bipolar transistor under no-signal conditions. If you want to use the device as a class-B amplifier, at which point should you bias it?
Test 3-5 Illustration for Part 3 Test Questions 30 and 31.
(a) Point V
(b) Point W
(c) Point X
(d) Point Y
(e) Point Z
31. In Fig. Test 3-5, point V portrays
(a) linear bias.
(b) cutoff.
(c) zero bias.
(d) saturation.
(e) pinchoff.
32. You can construct a push-pull amplifier with two identical JFETs, connecting the gates in phase opposition and connecting the drains
(a) in phase coincidence.
(b) 30° out of phase.
(c) 60° out of phase.
(d) 90° out of phase.
(e) in phase opposition as well.
33. In an FM signal, the extent to which the instantaneous signal amplitude varies is called
(a) zero, because it remains constant!
(b) the modulation index.
(c) the amplitude deviation.
(d) the amplitude fluctuation.
(e) the amplitude differential.
34. If we want a diode to completely block current in the reverse direction, we must ensure that
(a) the N type material has a more positive voltage than the P type material, and the peak applied voltage remains below the avalanche threshold.
(b) the N type material has a more negative voltage than the P type material, and the peak applied voltage remains below the avalanche threshold.
(c) the N type material has a more positive voltage than the P type material, and the peak applied voltage exceeds the avalanche threshold.
(d) the N type material has a more negative voltage than the P type material, and the peak applied voltage exceeds the avalanche threshold.
(e) the peak applied voltage never exceeds the alpha cutoff value.
35. Figure Test 3-6 shows how the gate voltage affects the drain current in a typical JFET. If you bias the device near the middle of the range marked X without inputting any signal, you have conditions good for
Test 3-6 Illustration for Part 3 Test Question 35.
(a) class-A amplification.
(b) class-B amplification.
(c) class-C amplification.
(d) class-D amplification.
(e) class-E amplification.
36. In most dielectric materials, radio waves travel at less than the speed of light, so the wavelength is shorter than it would be at the same frequency in air or a vacuum. For any given dielectric, the ratio of the shortened wavelength to the wavelength in air or a vacuum is called its
(a) wavelength ratio.
(b) speed ratio.
(c) velocity factor.
(e) frequency factor.
37. Figure Test 3-7 shows the schematic symbols for
Test 3-7 IIllustration for Part 3 Test Questions 37 and 38.
(a) N-channel (at A) and P-channel (at B) depletion-mode JFETs.
(b) N-channel and P-channel enhancement-mode JFETs.
(c) N-channel and P-channel depletion-mode MOSFETs.
(d) N-channel and P-channel enhancement-mode MOSFETs.
(e) nothing that we’ve discussed in this book, at least not yet.
38. The devices symbolized in Fig. Test 3-7 have
(a) extremely high input impedances.
(b) extremely low input impedances.
(c) excellent linearity but no way to produce any gain.
(d) high bias voltage requirements.
(e) no known characteristic; neither has appeared in this book, at least not yet.
39. What’s the decimal value of the quantity represented by the binary numeral 11011?
(a) 18
(b) 22
(c) 27
(d) 31
(e) 37
40. When you design and build a power supply, you can best minimize the risk of transient-related diode failure by
(a) inserting a timed switch that will reduce the AC input voltage for a few seconds after the transient occurs.
(b) using RF diodes instead of rectifier diodes.
(c) connecting a small-value resistor in parallel with each diode.
(d) placing a transient suppressor in the AC input line.
(e) using a transformer that can handle extremely high current.
41. How can we render the decimal quantity 45 in binary terms?
(a) 101101
(b) 100100
(c) 110001
(d) 100011
(e) 111011
42. Figure Test 3-8 is a time-domain graph illustrating the principle of
Test 3-8 Illustration for Part 3 Test Question 42.
(a) pulse-code modulation.
(b) pulse-amplitude modulation.
(c) pulse-duration modulation.
(d) pulse-interval modulation.
(e) pulse-width modulation.
43. You can increase the sensitivity of your HF radio receiver by
(a) using a squelch to silence the receiver when no signal comes in.
(b) placing a preamplifier between the antenna and the front end.
(c) reducing the voltage of the receiver’s power supply or battery.
(d) incorporating a balanced modulator to cancel out noise.
(e) adding a notch filter to increase the IF bandwidth.
44. For class-C power amplification, you should, under no-signal conditions, bias a bipolar transistor
(a) so drain current never flows, no matter how strong the input signal gets.
(b) somewhat beyond cutoff.
(c) exactly at cutoff.
(d) such that steady drain current flows.
(e) to saturation.
45. How many grids does a tetrode tube have?
(a) None
(b) One
(c) Two
(d) Three
(e) Four
46. Inside some pentode tubes, one of the grids is directly connected to the cathode. Which grid?
(a) The collector grid
(b) The control grid
(c) The screen grid
(d) The suppressor grid
(e) The gate grid
47. In a class-A JFET amplifier, a small change in the instantaneous gate voltage should produce
(a) a large change in the instantaneous drain voltage.
(b) an even smaller change in the instantaneous source voltage.
(c) a large change in the instantaneous channel current.
(d) an equivalent change in the instantaneous channel voltage.
(e) no change in the instantaneous channel current.
48. A grounded-grid amplifier using a triode vacuum tube
(a) is less likely to oscillate than a grounded-cathode amplifier.
(b) needs less driving power than a grounded-cathode amplifier.
(c) has high input impedance, making it ideal for weak-signal RF amplification.
(d) can operate with far lower voltage than a grounded-cathode amplifier.
(e) All of the above
49. In the hexadecimal numeration system, what follows A as you count upward?
(a) Nothing; that system has no digit A.
(b) B
(c) C
(d) D
(e) 10
50. The charge carriers in a vacuum tube are
(a) protons.
(b) neutrons.
(c) holes.
(d) electrons.
(e) ions.