Gibilisco S. Teach Yourself Electricity and Electronics
Подождите немного. Документ загружается.
16. Suppose an RF power amplifier has a dc collector input of 60 W, and is 75 percent efficient.
What is the RF signal output power?
(a) 80 W
(b) 60 W
(c) 45 W
(d) 40 W
(e) Impossible to determine from this data
17. If a listener is not expecting any change in the intensity of a signal or sound, the smallest
change that can be noticed is approximately which of the following?
(a) ⫾0.3 dB
(b) ⫾1 dB
(c) ⫾3 dB
(d) ⫾10 dB
(e) ⫾30 dB
18. A common base circuit is commonly employed as
(a) a microwave oscillator.
(b) a low-pass filter.
(c) a noise generator.
(d) a phase-locked loop.
(e) an RF power amplifier.
19. A semiconductor material especially noted for its photoconductivity, and which is often used
in making photocells, is
(a) selenium.
(b) lithium salt.
(c) copper chloride.
(d) aluminum oxide.
(e) polyethylene.
20. Which type of PA circuit provides the highest efficiency when used with the appropriate
amount of driving power?
(a) Class A
(b) Class AB
(c) Class B
(d) Class C
(e) All of the above circuits are equally efficient.
21. Baudot is a form of
(a) video modulation.
(b) diode.
Test: Part 3 461
(c) digital code.
(d) voice modulation.
(e) AM detector.
22. The most stable type of oscillator circuit uses
(a) a tapped coil.
(b) a split capacitor.
(c) negative feedback.
(d) a common base arrangement.
(e) a quartz crystal.
23. If the source-gate junction in an FET conducts,
(a) it is a sign of improper bias.
(b) the device will work in class C.
(c) the device will oscillate.
(d) the device will work in class A.
(e) the circuit will have good stability.
24. What is the radix of the octal number system?
(a) 2
(b) 2
2
(c) 2
3
(d) 2
4
(e) 2
5
25. Signal-to-noise ratio (S/N) is often specified when stating
(a) the selectivity of a receiver.
(b) the stability of an oscillator.
(c) the modulation coefficient of a transmitter.
(d) the sensitivity of a receiver.
(e) the polarization of an EM wave.
26. In a reverse-biased semiconductor diode, the junction capacitance depends on
(a) the width of the depletion region.
(b) the reverse current.
(c) the P:N ratio.
(d) the gate bias.
(e) the avalanche voltage.
27. Suppose the bandwidth of the channel in a receiver’s IF filter is 4.5 kHz at 30-dB power
attenuation, and 3.0 kHz at 3-dB power attenuation. What is the shape factor?
(a) 10:1
(b) 1.5:1
462 Test: Part 3
(c) 1:1
(d) 1:10
(e) More information is necessary to determine this.
28. A simple power supply filter can be built with
(a) a capacitor in series with the dc output.
(b) an inductor in parallel with the dc output.
(c) a rectifier in parallel with the dc output.
(d) a resistor in series and an inductor in parallel with the dc output.
(e) a capacitor in parallel with the dc output.
29. Which of the following bipolar transistor circuits can, in theory, provide the most
amplification?
(a) Common emitter
(b) Common base
(c) Common collector
(d) Common gate
(e) Common drain
30. The ratio of the difference in I
C
to the difference in I
B
that occurs when a small signal is
applied to the base of a bipolar transistor is called the
(a) static current amplification.
(b) dynamic current amplification.
(c) power factor.
(d) efficiency.
(e) current attenuation factor.
31. An example of a device that is commonly used as an oscillator at microwave frequencies is
(a) a rectifier diode.
(b) a weak-signal diode.
(c) a Gunn diode.
(d) a Zener diode.
(e) an avalanche diode.
32. In the operation of a PNP bipolar transistor, which of the following is normal concerning the
emitter and collector voltages?
(a) The collector is positive relative to the emitter.
(b) The collector is at the same voltage as the emitter.
(c) The collector is negative relative to the emitter.
(d) The collector can be either positive or negative relative to the emitter.
(e) The collector must be at ground potential.
Test: Part 3 463
33. What can be done to minimize the capacitance of the P-N junction in a semiconductor
diode, thereby making the component effective as a high-speed RF switch?
(a) The surface area of the P-N junction can be maximized.
(b) A layer of intrinsic semiconductor can be placed between the P- and N-type materials.
(c) The frequency of the applied signal can be made as high as possible.
(d) The diode can be forward-biased with a high voltage.
(e) A small-value resistor can be connected in series with each of several diodes, and the series
diode-resistor combinations can all be connected in parallel.
34. Which type of modulation consists of one voice sideband, with a suppressed carrier?
(a) AM
(b) LSB
(c) FM
(d) RTTY
(e) PCM
35. Suppose a series-parallel network of resistors is assembled into an RF attenuator pad, which is
a circuit deliberately intended to produce a constant signal loss over a wide band of frequencies. If
the input RF voltage to this attenuator pad is 500 µV and the output RF voltage is 100 µV, what
is the loss in decibels?
(a) 14.0 dB
(b) 6.99 dB
(c) 5.00 dB
(d) 1.40 dB
(e) 0.699 dB
36. In an AND gate, the output is high
(a) if any input is high.
(b) only when all inputs are low.
(c) if any input is low.
(d) only when all inputs are high.
(e) only when all inputs have identical logic states.
37. A voltage-controlled oscillator makes use of
(a) a varactor diode.
(b) a Zener diode.
(c) negative feedback.
(d) a split capacitance.
(e) adjustable gate or base bias.
38. The best electrical ground for a power supply is obtained by
(a) connecting a small-value capacitor between the hot wire and a good earth ground, such as
an 8-ft copper rod driven into the earth.
464 Test: Part 3
(b) ensuring that the ground wire from the power supply is connected to the third wire hole
in one of the utility outlets of a properly installed three-wire electrical circuit.
(c) using a center-tapped transformer and a full-wave rectifier circuit, in conjunction with
good filtering, voltage regulation, and transient suppression.
(d) connecting a large-value inductor in series with the hot wire, thereby ensuring that the
voltage on that wire cannot be shunted to ground.
(e) making sure that all equipment connected to the supply is provided with fuses and/or
circuit breakers of the proper ratings.
39. Suppose the output signal voltage from an amplifier is 35 times the input signal voltage. If
the input and output impedances are both pure resistances of the same value, what is the gain?
(a) 15 dB
(b) 31 dB
(c) 35 dB
(d) 350 dB
(e) 700 dB
40. In an exclusive OR gate, the output is high
(a) if either input is high.
(b) only when both inputs are low.
(c) if either input is low.
(d) only when both inputs are high.
(e) only when the inputs have opposite logic states.
41. A ratio detector is a circuit for demodulating which of the following?
(a) AM
(b) PM
(c) FM
(d) SSB
(e) AFSK
42. Suppose there is a binary digital black box with two inputs, called X and Y, and an output
called Z. If X = 0 and Y = 1, then Z = 0. In all other instances, Z = 1. Which of the following
logical expressions represents the contents of the black box?
(a) X + (−Y)
(b) X * (−Y)
(c) X − (*Y)
(d) X = (−Y)
(e) X − (+Y)
43. A method of modulation in which the strength of pulses varies is called
(a) pulse ratio modulation.
(b) pulse position modulation.
Test: Part 3 465
(c) pulse frequency modulation.
(d) pulse amplitude modulation.
(e) pulse width modulation.
44. Boolean algebra is
(a) useful for calculating amplifier gain in decibels.
(b) a useful tool in binary digital circuit design.
(c) used to calculate the value of an unknown.
(d) used with negative pulse modulation schemes.
(e) used with positive pulse modulation schemes.
45. A voltage-doubler power supply is best for use in
(a) circuits that need high voltage but do not draw much current.
(b) low-voltage devices.
(c) high-current appliances.
(d) all kinds of electronic equipment.
(e) broadcast transmitter power amplifiers.
46. An optoisolator consists of
(a) two Zener diodes back-to-back.
(b) an LED and a photodiode.
(c) two NPN transistors in series.
(d) an NPN transistor followed by a PNP transistor.
(e) a PNP transistor followed by an NPN transistor.
47. When a semiconductor is reverse-biased with a large enough voltage, it will conduct. This
phenomenon is known as
(a) bias effect.
(b) avalanche effect.
(c) forward breakover.
(d) saturation.
(e) conduction effect.
48. Synchronizing pulses in a conventional analog TV signal
(a) keep the brightness constant.
(b) keep the contrast constant.
(c) keep the image from tearing or rolling.
(d) ensure that the colors are right.
(e) keep the image in good focus.
49. In an enhancement-mode MOSFET,
(a) the channel conducts fully with zero gate bias.
(b) the channel conducts partially with zero gate bias.
466 Test: Part 3
(c) the channel conducts ac but not dc.
(d) the channel conducts dc but not ac.
(e) the channel does not conduct with zero gate bias.
50. In a step-up power transformer,
(a) the primary voltage is more than the secondary voltage.
(b) the secondary voltage is more than the primary voltage.
(c) the primary and secondary voltages are the same.
(d) the secondary must be center-tapped.
(e) the primary must be center-tapped.
Test: Part 3 467
This page intentionally left blank
4
PART
Specialized Devices
and Systems
Copyright © 2006, 2002, 1997, 1993 by The McGraw-Hill Companies, Inc. Click here for terms of use.
This page intentionally left blank