Deck 7: Basic BJT Amplifiers

Question 1

It is standard practice to use capital letters and subscripts for dc quantities.

Answer 1

True

Question 2

Distortion is desirable in high-fidelity amplifiers because it changes the sound of voice and music.

Answer 2

False

Question 3

The ac current gain equals the ac collector current divided by the ac base current.

Answer 3

True

Question 4

The unbypassed emitter resistance is called a feedback resistor because it has an ac voltage across it that opposes changes in voltage gain.

Question 5

When coupling an ac signal from stage to stage,the capacitive reactance should be at least

A) 10 times smaller than the resistance at the lowest frequency of operation.
B) 100 times smaller than the resistance at the lowest frequency of operation.
C) 10 times larger than the resistance at the lowest frequency of operation.
D) 10 times smaller than the resistance at the highest frequency of operation.

Question 6

The voltage gain of an amplifier is defined as the ac output voltage divided by the ac input voltage.

Question 7

A bypass capacitor is similar to a coupling capacitor because it appears open to dc and shorted to ac.

Question 8

Coupling capacitors can be approximated as dc shorts.

Question 9

The common-emitter amplifier can be recognized by noting that the emitter is at dc ground.

Question 10

If there is any ac voltage at an amplifier's bypass emitter,it means that the

A) transistor is shorted.
B) transistor is open.
C) coupling capacitor is open.
D) bypass capacitor is open.

Question 11

A coupling capacitor couples an ac signal into an amplifier without disturbing its operating point.

Question 12

Voltage gain is ac output voltage divided by the ac input voltage.

Question 13

The impedance of a capacitor is inversely proportional to the frequency and the capacitor effectively blocks dc voltage.

Question 14

The voltage gain equals the ac collector resistance divided by the ac resistance of the collector diode.

Question 15

The ac equivalent circuit model called the Ebers-Moll looks like a P on its side and is sometimes called a P model.

Question 16

One way to reduce distortion in a transistor amplifier is to keep the base ac input voltage small.

Question 17

What is the mathematical approach that models the transistor on what is happening at its terminals without regard for the physical processes taking place inside the transistor?

A) small-signal characteristics
B) Thevenin's Theorem
C) Kirchoff's Laws
D) h parameters

Question 18

One way to stabilize voltage gain is to leave some of the emitter resistance unbypassed.

Question 19

The ac resistance of the emitter diode equals the ac base-emitter voltage divided by the ac emitter current.

Question 20

Discrete means all components like resistors,capacitors,and transistors are created and connected on a chip,a piece of semiconductor material.

Question 21

The stretching and compressing of alternate half cycles at the output of a transistor amplifier is called ________.

A) oscillation
B) amplification
C) distortion
D) extortion

Question 22

The reactance of a coupling capacitor at dc voltage is ________.

A) zero
B) infinite
C) 100 kW
D) 1.414 W

Question 23

Distortion is undesirable in high-fidelity amplifiers because

A) it changes the sound of voice and music.
B) it amplifies the sound of voice and music.
C) it trips a circuit breaker.
D) it cannot be heard in either speaker.

Question 24

The simplest way to analyze an amplifier is to split the analysis into what two parts?

A) schematics and values
B) amplifiers and oscillators
C) dc and ac
D) semiconductors and conductors

Question 25

In order to calculate the collector current for the circuit shown in Figure 8-2 (a),you must

A) divide 15 V by 100.
B) multiply the base current by 100.
C) multiply 0.7 V by 100.
D) divide 30 V by 5 kW.

Question 26

In transistor amplifier notation,lowercase letters and subscripts are used for

A) dc quantities.
B) ac quantities.
C) schematic symbols.
D) labeling filters.

Question 27

What is the term that describes components such as resistors,capacitors,and transistors that are separately inserted and connected to get a final circuit?

A) discrete
B) integrated
C) chip
D) printed circuit

Question 28

The ac collector current divided by the ac base current is referred to as

A) dc current gain.
B) ac current gain.
C) alpha.
D) delta.

Question 29

What is a method used to analyze an amplifier in which each source is calculated separately while the other source is reduced to zero?

A) Kirchoff's Laws
B) Fourier's analysis
C) Lenz's Law
D) superposition

Question 30

When a single or double stage amplifier is not working,troubleshooting can begin by measuring dc voltages.

Question 31

In order for a bypass capacitor to work properly,its reactance must be

A) much smaller than the resistance.
B) much larger than the resistance.
C) equal to the resistance.
D) infinite.

Question 32

In a well-designed coupling circuit,the coupling capacitor approximates

A) an ac open.
B) a dc short.
C) a dc open.
D) an ac short.

Question 33

A swamped amplifier decreases input impedance and increases distortion.

Question 34

The ac output voltage of an amplifier divided by the ac input voltage is referred to as the amplifier's

A) power output.
B) power gain.
C) voltage gain.
D) beta.

Question 35

The ac base-emitter voltage divided by the ac emitter current equals

A) ac resistance.
B) dc resistance.
C) reactance.
D) impedance.

Question 36

When all components are simultaneously created and connected on a piece of semiconductor material,it is referred to as what kind of circuit?

A) discrete
B) integrated
C) chat
D) protection

Question 37

What is one way to minimize distortion?

A) use batteries only
B) keep amplifier dc supply voltages low
C) use ICs
D) keep ac base voltages small

Question 38

An equivalent transistor circuit model used to analyze ac signal processing that looks like a T on its side is the

A) Fourier model.
B) p model.
C) Thevenin model.
D) Ebers-Moll model.

Question 39

What is the most popular circuit model that is used to analyze how a transistor behaves when an ac signal is present?

A) Fourier model.
B) p model.
C) Thevenin model.
D) Ebers-Moll model.

Question 40

The base current for the circuit shown in Figure 8-2 (a)can be determined by

A) dividing 100 by 5 kW.
B) dividing 30 V by 5 kW.
C) dividing 30 V by 1 MW.
D) dividing 15 V by 100.

Question 41

In the circuit shown in Figure 8-4,what effect do the capacitors have on the dc biasing?

A) add 0.7 V
B) add 15 V
C) puts transistor in cutoff
D) no effect

Question 42

In the circuit shown in Figure 8-30,if the collector voltage is 0 V and the base voltage is 0 V,what is the trouble?

A) 1 mV generator open
B) C₁ open
C) C₃ shorted
D) +10 V supply is faulty

Question 43

If excessive hum is heard coming out of a loudspeaker,one of the prime suspects is a shorted diode in the power supply.

Question 44

What makes the p model,an equivalent transistor circuit model,easier to use than other models?

A) it shows input impedance
B) it uses Ohm's Law
C) it uses calculus
D) it shows output impedance

Question 45

In the circuit shown in Figure 8-30,if the ac collector voltage is 2 mV and the dc collector voltage is 6 V,what is the trouble?

A) C₁ is shorted
B) C₁ is open
C) +10 V supply is faulty
D) 2.2 kΩ resistor is open

Question 46

The amplifier shown in Figure 8-4 is

A) an emitter-biased amplifier.
B) a base-biased amplifier.
C) a common collector.
D) an emitter follower.

Question 47

Amplified ripple out of a loudspeaker is detected as

A) sine waves.
B) high pitch noise.
C) high frequency signals.
D) low frequency hum.

Question 48

In the circuit shown in Figure 8-8,if an ac voltage was measured between the emitter and ground

A) this is normal.
B) this means the amplifier is in cutoff.
C) this means that the bypass capacitor is open.
D) this means the transistor is open.

Question 49

Which statement is true with regard to the circuit shown in Figure 8-4?

A) the ac signal out of the transistor is amplified and inverted
B) the ac signal out of the transistor is amplified and in-phase with the input
C) the ac signal out of the transistor is not amplified
D) the ac signal out of the transistor is attenuated

Question 50

The circuit shown in Figure 8-30 has an ac emitter voltage of 0.75 mV and an ac collector voltage of 5 mV.What is the trouble?

A) C₃ open
B) C₃ shorted
C) C₂ open
D) C₂ shorted

Question 51

A bypass capacitor appears

A) shorted to dc.
B) open to ac.
C) open to dc.
D) like a semiconductor.

Question 52

Using the values listed on the circuit shown in Figure 8-8,what is the approximate value for the collector current?

A) 20 mA
B) 1 mA
C) 1 mA
D) 10 m