Electronic Devices 10th Edition by Thomas L. Floyd – Test Bank

 

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            Sample Questions

 

 

Exam
Name___________________________________

TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
1) The base region of a BJT is heavily doped and wide compared to the other two regions.

1)

2) When a BJT is conducting, the collector current is identical to the emitter current.

2)

3) The βDC for a BJT is the ratio of collector current to emitter current.

3)

4) A saturated BJT has maximum collector current.

4)

5) Assume a transistor has a maximum power rating of 1 W and VCE = 5 V. If IC = 120 mA, the power

5)

rating is not exceeded.
6) The voltage gain of a BJT amplifier is directly proportional to the internal ac emitter resistance.

6)

7) Photo transistors have the greatest sensitivity to blue light.

7)

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
8) In a certain BJT, the collector current is 22.0 mA when the base current is 100 μA. The emitter
current is
A) 22.0 mA
B) 22.1 mA
C) 21.9 mA
D) 2.2 mA

8)

9) The value of βDC is the ratio of

9)

A) emitter current to base current
C) collector current to base current

B) collector current to emitter current
D) none of the above

10) Typical values of αDC are from
A) 20 to 200

10)

B) 0.95 to 0.99

C) 800 to 1000

D) 1.00 to 10

11) A forward-biased npn transistor has a typical voltage drop from base to emitter of
A) 50 V
B) 0.7 V
C) 1.5 V
D) 10 V

1

11)

Figure 1
12) Refer to Figure 1. Assume βDC = 200. The expected value of IB is
A) 200 μA

B) 161 μA

12)

C) 80 μA

D) 182 μA

13) Refer to Figure 1. Assume βDC = 200. The value of VCE is approximately
A) 12.4 V

B) 5.8 V

C) 9.2 V

13)
D) 7.5 V

14) Refer to Figure 1. If VCC is increased to 18 V, IB will
A) decrease

B) increase

14)
C) not change

2

Figure 2 A characteristic curve
15) For the characteristic curve in Figure 2, the region between A and B is called the
A) saturation region
B) cutoff region
C) breakdown region
D) active region

15)

16) For the characteristic curve in Figure 2, the equation IC = βDCIB is true

16)

A) only beyond C on the curve
C) only between A and B on the curve

B) only between B and C on the curve
D) at no place on the curve

17) ICEO is

17)

A) collector current when the transistor is saturated
B) collector current when the transistor is on
C) collector current when the transistor is cutoff
D) base current when the transistor is saturated
18) If a BJT is saturated,
A) both base current and collector current are at a maximum
B) base current is at maximum
C) VCC appears between the collector and emitter

18)

D) collector current is at maximum
19) If a BJT is saturated,
A) VCE is approximately 1/2 VCC

19)
B) VCE is approximately equal to VCC

C) VCE is near zero

D) none of the above

3

Figure 3 The transistor has the following ratings: PD(max) = 650 mW, VCE(max) = 40 V, and IC(max) = 200 mA.
20) Refer to Figure 3. The maximum value that VCC can be adjusted to without exceeding the
VCE(max) rating is (ignore other max ratings).
A) 60 V
B) 50 V

C) 40 V

D) 45 V

21) Refer to Figure 3. If VCC is set to 48 V, PD(max) is exceeded by
A) 80 mW

B) 310 mW

21)

C) 55 mW

D) 110 mW

22) Refer to Fig 3. Assume VCC is lowered to 15 V. The transistor is
A) in the linear range

B) cutoff

22)
C) saturated

23) The symbol h FE means the same as
A) Av

20)

23)

B) αDC

C) β DC

D) PD(max)

24) h FE varies with

24)

A) temperature
C) both A and B

B) collector current
D) none of the above

25) A 10 mV ac signal is applied to the base of a properly biased transistor with RC = 1.2 kΩ and re’ =
36 Ω. The output ac voltage is
A) 33 mV
B) 333 mV

C) 152 mV

4

D) 105 mV

25)

Figure 4
26) Refer to Figure 4. Assume RB = 22 kΩ. The collector current will be approximately
A) 10 mA

B) 27 mA

C) 5 mA

26)

D) 20 mA

27) Refer to Figure 4. The largest base resistor that will still saturate the transistor is approximately
A) 400 kΩ
B) 330 kΩ
C) 40 kΩ
D) 33 kΩ

27)

28) Refer to Figure 4. If R B = 100 kΩ, VC is approximately

28)

A) 12.5 V

B) 7.5 V

C) 5 V

D) 10 V

29) Refer to Figure 4. If you wanted to change the transistor to a pnp type, you need to
A) increase the collector resistor
B) increase the base resistor
C) change both dc sources to negative supplies
D) all of the above

5

29)

Figure 5
30) Refer to Figure 5. When conducting, assume the LED drops 1.8 V and VCE(sat) = 0.2 V. If the input
square wave is +3.0 V, the current in the LED will be approximately
A) 30 mA
B) 136 mA
C) 105 mA

30)

D) 24 mA

31) The NAND gate is a digital circuit that produces a
A) HIGH level signal when both inputs are LOW
B) HIGH level signal when both inputs are HIGH
C) LOW level signal when both inputs are HIGH
D) LOW level signal when both inputs are LOW

31)

32) The NOR gate is a digital circuit that produces a
A) HIGH level signal when one or more inputs are HIGH
B) HIGH level signal when one or more inputs are LOW
C) LOW level signal when one or more inputs are HIGH
D) LOW level signal when one or more inputs are LOW

32)

33) In switching circuits, a transistor operates between
A) active region and breakdown
C) cutoff and active region

33)
B) cutoff and saturation
D) none of the above

34) The light sensitive region of a photo transistor is the
A) collector
B) substrate

6

34)
C) base

D) emitter

Figure 6 A phototransistor and its characteristic curve
35) Refer to Figure 6. Assume you measure VOUT as 11 V. From this, you can conclude that the light
intensity is approximately
A) 30 mW/cm2

B) 20 mW/cm2

C) 10 mW/cm2

36) The primary purpose of an optocoupler is to
A) isolate certain sections of circuits
C) convert light into electrical current

35)

D) 40 mW/cm2
36)

B) amplify light
D) couple an LED to a relay

37) The metal mounting tab or case of a power transistor is connected to the
A) substrate
B) base
C) collector
38) Small signal transistors are available in
A) dual in line (DIP) packs
C) plastic or metal cases

37)
D) emitter
38)

B) quad small outline (SO) packs
D) all of the above

7

Figure 7
39) Refer to Figure 7. Assume a single problem accounts for the readings. From the readings, you can
conclude that
A) the base-emitter junction is open
B) R B is open
C) the base-collector junction is open

39)

D) R C is shorted

40) Refer to Figure 7. The transistor is
A) saturated
C) in the active region

40)
B) in the breakdown region
D) cutoff

8

Exam
Name___________________________________

TRUE/FALSE. Write ‘T’ if the statement is true and ‘F’ if the statement is false.
1) A class-A amplifier the quiescent power is dissipated only when a signal is present.

1)

2) The maximum power from a class-A amplifier is equal to ICQVCEQ.

2)

3) The ratio of Pout to PDC is the efficiency of an amplifier.

3)

4) In a class-B amplifier, the Q-point is at cutoff.

4)

5) A class-B amplifier with Darlington transistors can use larger bias resistors.

5)

6) Class-C amplifiers are frequently used as audio amplifiers.

6)

7) The Q point of a class-C amplifier is below cutoff.

7)

MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.
8) In a single-stage class-A amplifier, the quiescent current is the same as the
A) ac load current
B) ac collector current
C) dc collector current
D) bias current
9) The maximum ideal efficiency for a class-A amplifier is
A) 55%
B) 25%
C) 40%

8)

9)
D) 80%

10) Assume the Q point on a class-A amplifier is centered on the ac load line. The maximum
peak-to-peak output voltage is
A) 2 VCEQ
B) VCEQ
C) 1/2 VCC
D) 1/2 VCEQ

1

10)

Figure 1
11) Refer to Figure 1. The dc collector current is approximately
A) 85 mA
B) 120 mA
C) 50 mA

D) 25 mA

11)

12) Refer to Figure 1. The input impedance is approximately
A) 186 Ω
B) 125 Ω
C) 142 Ω

D) 230 Ω

12)

13) Refer to Figure 1. The voltage gain, Av , to the load is approximately
A) 11

B) 5.4

C) 7.5

13)
D) 2.0

14) Refer to Figure 1. The power gain, Ap , to the load is approximately
A) 14

B) 7.9

C) 23

2

14)
D) 4.5

Figure 2 This is modification of Figure 1 (added Q2 , Q3 , and RL, deletion of C3 and a changed value of RE1).
15) Refer to Figure 2, which is a modified circuit from Figure 1. The voltage gain, AV, of this circuit is
approximately
A) 5.6

B) 2.0

C) 3.3

D) 4.3

16) Refer to Figure 2. If Vin = 1 Vrms, the ac power in RL is approximately
A) 2.6 W

B) 680 mW

C) 1.3 W

15)

16)
D) 4.0 W

17) Refer to Figure 2. With no applied signal, the dc power dissipated in the load is approximately
A) 1.1 W
B) 2.8 W
C) 5.5 W
D) 0

17)

18) Refer to Figure 2. Assume Vout has dropped to about 1/2 the expected value. A likely cause is that

18)

A) RL is open

B) C 2 is shorted

C) VCC is set to +15 V

D) C 2 is open

3

Figure 3
19) Refer to Figure 3. This type of bias is called
A) diode biasing
C) current-mirror biasing

19)
B) push-pull bias
D) mid-point bias

20) Refer to Figure 3. The value of dc bias current in R1 is
A) 48 mA

B) 86 mA

20)
C) 43 mA

D) 90 mA

21) Refer to Figure 3. With no signal in, IC(Q1) is ideally
A) 48 mA

B) 0

21)
C) 86 mA

D) 43 mA

22) Refer to Figure 3. Note the input is a 5 Vrms sine wave. The ac power in RL is ideally
A) 1.56 W

B) 0.31 W

C) 0.62 W

23) A heat sink is used to
A) prevent excessive current
C) reduce ambient temperature

22)

D) 3.12 W
23)

B) reduce the junction temperature
D) all of the above

4

24) In a class-AB amplifier, the transistors are biased slightly above cutoff to avoid
A) clipping the peaks of signals
B) low efficiency
C) crossover distortion
D) loading problems

24)

25) A class-A amplifier has an input resistance of 520 Ω and a load resistance of 26 Ω. Assume a 1 Vrms

25)

input produces a 5 Vrms output The power gain is
A) 100

B) 500

C) 5

D) 50

Figure 4
26) Refer to Figure 4. The amplifier represented is
A) class-B
B) class-A

26)
C) class-C

27) The amplifier type that has the worst efficiency is
A) class-AB
B) class-B

27)
C) class-A

D) class-C

28) The amplifier type that frequently has a resonant circuit load is
A) class-AB
B) class-A
C) class-B

D) class-C

5

28)

Figure 5
29) Refer to Figure 5. The diode
A) produces class-AB operation
B) helps prevent crossover distortion
C) compensates for the base-emitter drops of the transistors
D) all of the above

29)

30) Refer to Figure 5. The center tap on the output transformer (marked A) should be connected to
A) +VCC
B) ground

30)

C) −VCC

D) nothing, it is left open

Figure 6
31) Refer to Figure 6. The combination of R1 , C 1, and the base-emitter diode form a
A) negative clipping circuit
C) coupling circuit

B) clamping circuit
D) positive clipping circuit

6

31)

32) The transistor in a Class-C amplifier is biased for conduction for
A) 90°
B) 180°
C) 360°
D) much less than 90°

32)

Figure 7
33) Refer to Figure 7. The expected dc emitter voltage for Q1 is
A) 9.0 V

B) 0.7 V

C) 8.3 V

33)
D) 0 V

34) Refer to Figure 7. The expected ac emitter voltage for Q1 is
A) 2.0 Vrms

B) 4.0 Vrms

C) 0 V

D) none of the above

35) Refer to Figure 7. The power delivered to the load is
A) 1 W
B) 0.25 W

7

34)

35)
C) 0.5 W

D) 2 W