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Multiple choice question for engineering

Set 1

(Q.1-Q.6) consider the figure shown below and answer the questions that proceed.
electronic-devices-circuits-questions-answers-biasing-bjt-amplifier-circuits-q1

1. For Vcc = 15V, R1 = 100 kΩ, R(E) = 3.9 kΩ, R(C) = 6.8 kΩ and ß = 100, determine the dc collector current for each transistor.
a) 0.29 mA
b) 0.48 mA
c) 0.96 mA
d) 1.92 mA

View Answer

Answer: c [Reason:] electronic-devices-circuits-questions-answers-biasing-bjt-amplifier-circuits-q1a

2. For Vcc = 15V, R1 = 100 kΩ, R(E) = 3.9 kΩ, R(C) = 6.8 kΩ and ß = 100, determine the dc collector voltage for each transistor.
a) 4.25 V
b) 8.5 V
c) 12.75 V
d) 17 V

View Answer

Answer: b [Reason:] electronic-devices-circuits-questions-answers-biasing-bjt-amplifier-circuits-q1a

3. Find R (in 1) for R (sig) = 5 kΩ.
a) 2.4 kΩ
b) 4.8 kΩ
c) 17.3 kΩ
d) 34.6 kΩ

View Answer

Answer: a [Reason:] It is the parallel combination of the 32 kΩ resistor and 2.6 kΩ resistor respectively.

4. Find Vb1/Vsig for R(sig) = 5 kΩ.
a) 0.08 V/V
b) 0.16 V/V
c) 0.24 V/V
d) 0.32 V/V

View Answer

Answer; d [Reason:] electronic-devices-circuits-questions-answers-biasing-bjt-amplifier-circuits-q4

5. Find R (in 2).
a) 2.4 kΩ
b) 4.8 kΩ
c) 17.3 kΩ
d) 34.6 kΩ

View Answer

Answer: a [Reason:] It is the parallel combination of the 32 kΩ resistor and 2.6 kΩ resistor respectively.

6. Find Vb2/Vb1.
a) -34 V/V
b) -51 V/V
c) – 68.1 V/V
d) -100 V/V

View Answer

Answer: c [Reason:] electronic-devices-circuits-questions-answers-biasing-bjt-amplifier-circuits-q6

7. For Rl = 2 kΩ find Vo/Vb2.
a) -59.3 V/V
b) -29.7 V/V
c) -89.1 V/V
d) None of the mentioned

View Answer

Answer: a [Reason:] electronic-devices-circuits-questions-answers-biasing-bjt-amplifier-circuits-q7

8. Find the overall voltage gain.
a) 323 V/V
b) 646 V/V
c) 969 V/V
d) 1292 V/V

View Answer

Answer: d [Reason:] electronic-devices-circuits-questions-answers-biasing-bjt-amplifier-circuits-q8

Set 2

1. Find the maximum allowed output negative swing without the transistor entering saturation, and
a) 1.27 mV
b) 1.47 mV
c) 1.67 mV
d) 1.87 mV

View Answer

Answer: d [Reason:] electronic-devices-circuits-questions-answers-bjt-amplifier-design-q1

2. The corresponding maximum input signal permitted is
a) 1.64 mV
b) 1.74 mV
c) 1.84 mV
d) 1.94 mV

View Answer

Answer: d [Reason:] If we assume linear operation right to saturation we can use the gain Av to calculate the maximum input signal. Thus for an output swing ∆ Vo = 0.8 we have ∆ Vi = ∆ Vo / Av = -0.7 / -360 = 1.94 mV.

(Q.3- Q.5) For the amplifier circuit in Fig. 6.33(a) with Vcc = +10 V, Rc = 1 kΩ and the DC collector bias current equal to Ic,

3. Find the voltage gain.
a) 100 Ic
b) 200 Ic
C) 400 Ic
d) 800 Ic

View Answer

Answer: c [Reason:] electronic-devices-circuits-questions-answers-bjt-amplifier-design-q3

4. The maximum possible positive output signal swing as determined by the need to keep the transistor in the active region.
a) 9.7 + Ic
b) 9.7 – Ic
c) 10.3 + Ic
d) 10.3 – Ic

View Answer

Answer: a [Reason:] Assuming the output voltage Vo = 0.3v is the lowest Vce to stay out of saturation. Vo = 0.3 = 10 – IcRc = 10 – IcRc + ∆Vo ∆ Vo = -10 + 0.3 + Ic*1.

5. The maximum possible negative output signal swing as determined by the need to keep the transistor in the active region.
a) 0.1 Ic
b) Ic
c) 10 Ic
d) 100 Ic

View Answer

Answer: b [Reason:] Maximum output voltage before the Transistor is cutoff. Vce + ∆Vo = Vcc ∆Vo = Vcc – Vce = 10 – 10 + 10 Ic = 10 Ic.

6. The transistor in the circuit below is biased at a dc collector current of 0.5 mA. What is the voltage gain?
electronic-devices-circuits-questions-answers-bjt-amplifier-design-q6
a) -1 V/V
b) -10 V/V
c) -100 V/V
d) -1000 V/V

View Answer

Answer: c [Reason:] electronic-devices-circuits-questions-answers-bjt-amplifier-design-q6a

7. For a BJt Vt is 5 V, Rc = 1000 ohm and bias current Ic is 12 mA. The value of the voltage gain is __________
a) -1.2 V/V
b) -2.4 V/V
c) -3.6 V/V
d) -4.8 V/V

View Answer

Answer: b [Reason:] Voltage gain is (Ic X Rc ) / Vt.

(Q.8–Q.10) (Q.3- Q.5) For the BJT amplifier circuit with Vcc = +10 V, Rc = 1 kΩ and the DC collector bias current equal to 5 mA,

8. The value of the voltage gain is _______________
a) -2 V/V
b) -4 V/V
c) -10 V/V
d) -20 V/V

View Answer

Answer: a [Reason:] The voltage is 400 X Ic where Ic is 5 mA.

9. The maximum possible positive output signal swing as determined by the need to keep the transistor in the active region.
a) -1.7 V
b) -2.7 V
c) -3.7 V
d) -4.7 V

View Answer

Answer: d [Reason:] The maximum voltage swing is given by -10 + 0.3 + (Ic X Rc). Putting Ic as 5 mA, we get -4.7 mV.

10. The maximum possible negative output signal swing as determined by the need to keep the transistor in the active region.
a) 0.5 V
b) 1 V
c) 5 V
d) 10 V

View Answer

Answer: c [Reason:] It is given by -10 + 10 + (Ic X Rc). Putting Ic as 5 mA we get 5V.

Set 3

1. Which of the following condition is true for cut-off mode?
a) The collector current Is zero
b) The collector current is proportional to the base current
c) The base current is non zero
d) All of the mentioned

View Answer

Answer: a [Reason:] The base current as well as the collector current are zero in cut-off mode.

2. Which of the following is true for the cut-off region in an npn transistor?
a) Potential difference between the emitter and the base is smaller than 0.5V
b) Potential difference between the emitter and the base is smaller than 0.4V
c) The collector current increases with the increase in the base current
d) The collector current is always zero and the base current is always non zero

View Answer

Answer: b [Reason:] Both collector and emitter current are zero in cut-off region.

3. Which of the following is true for a typical active region of an npn transistor?
a) The potential difference between the emitter and the collector is less than 0.5 V
b) The potential difference between the emitter and the collector is less than 0.4 V
c) The potential difference between the emitter and the collector is less than 0.3 V
d) The potential difference between the emitter and the collector is less than 0.2 V

View Answer

Answer: c [Reason:] Most commonly used transistors have Vce less than 0.4 V for the active region.

4. Which of the following is true for the active region of an npn transistor?
a) The collector current is directly proportional to the base current
b) The potential difference between the emitter and the collector is less than 0.4 V
c) All of the mentioned
d) None of the mentioned

View Answer

Answer: c [Reason:] The base current and the collector current are directly proportional to each other and the potential difference between the collector and the base is always less than 0.4 V.

5. Which of the following is true for the saturation region of BJT transistor?
a) The collector current is inversely proportional to the base current
b) The collector current is proportional to the square root of the collector current
c) The natural logarithm of the collector current is directly proportional to the base current
d) None of the mentioned

View Answer

Answer: b [Reason:] The collector current is directly proportional to the base current in the saturation region of the BJT.

6. Which of the following is true for a npn transistor in the saturation region?
a) The potential difference between the collector and the base is approximately 0.2V
b) The potential difference between the collector and the base is approximately 0.3V
c) The potential difference between the collector and the base is approximately 0.4V
d) The potential difference between the collector and the base is approximately 0.5V

View Answer

Answer: d [Reason:] The commonly used npn transistors have a potential difference of around 0.5V between he collector and the base.

7. The potential difference between the base and the collector Vcb in a pnp transistor in saturation region is ________
a) -0.2 V
b) -0.5V
c) 0.2 V
d) 0.5 V

View Answer

Answer: b [Reason:] The value of Vcb is -0.5V for a pnp transistor and 0.5V for an npn transistor.

8. For a pnp transistor in the active region the value of Vce (potential difference between the collector and the base) is
a) Less than 0.3V
b) Less than 3V
c) Greater than 0.3V
d) Greater than 3V

View Answer

Answer: a [Reason:] For a pnp transistor Vce is less than 0.3V, for an npn transistor it is greater than 0.3V.

9. Which of the following is true for a pnp transistor in active region?
a) CB junction is reversed bias and the EB junction is forward bias
b) CB junction is forward bias and the EB junction is forward bias
c) CB junction is forward bias and the EB junction is reverse bias
d) CB junction is reversed bias and the EB junction is reverse bias

View Answer

Answer: a [Reason:] Whether the transistor in npn or pnp, for it be in active region the EB junction must be reversed bias the CB junction must be forward bias.

10. Which of the following is true for a pnp transistor in saturation region?
a) CB junction is reversed bias and the EB junction is forward bias
b) CB junction is forward bias and the EB junction is forward bias
c) CB junction is forward bias and the EB junction is reverse bias
d) CB junction is reversed bias and the EB junction is reverse bias

View Answer

Answer: b [Reason:] Whether the transistor in npn or pnp, for it be in saturation region the EB junction must be forward bias the CB junction must be forward bias.

Set 4

1. The curve between the collector current versus the potential difference between the base and emitter is
a) A straight line inclined to the axes
b) A straight line parallel to the x-axis
c) An exponentially varying curve
d) A parabolic curve

View Answer

Answer: c [Reason:] The natural logarithm of the collector current depends directly on the the potential difference between the base and the emitter.

2. The curve between the collector current and the saturation is
a) A straight line inclined to the axes
b) A straight line parallel to the x-axis
c) A straight line parallel to the y-axis
d) An exponential curve

View Answer

Answer: a [Reason:] The collector current depends directly on the saturation current.

3. The magnitude of the thermal voltage is given by
a) k/Tq
b) kT/q
c) q/Kt
d) Tk/q

View Answer

Answer: b [Reason:] kT/q is the correct mathematical expression for the thermal voltage.

4. The correct relation between the transistor parameters α and ß are related by
a) ß = 1 – α/α
b) ß = 1 + α/α
c) α = ß + 1/ß
d) α = ß/ß + 1

View Answer

Answer: d [Reason:] Only expression α = ß/ß + 1 is the correct expression that relates α and ß.

5. The correct expression relating the emitter current Ie to the collector current Ic is
a) Ie = α Ic
b) Ic = α Ic
c) Ie = ß Ic
d) Ic = ß Ic

View Answer

Answer: b [Reason:] Ie = Ic/α or Ic = α Ie

6. The value of the thermal voltage at room temperature can be approximated as
a) 25 mV
b) 30 mV
c) 35 mV
d) 40 mV

View Answer

Answer: a [Reason:] Thermal voltage is given by kT/q which at T = 25 degrees Celsius is approximately 25 mV.

7. The correct relation between the emitter current Ie and the base current Ib is given by
a) Ib = (1 + α) Ie
b) Ib = (α – 1) Ie
c) Ie = (1 – ß) Ib
d) Ie = (1 + ß) Ib

View Answer

Answer: d [Reason:] The correct mathematical expression are Ie = (1 – ß) Ib and Ib = (1 – α) Ie respectively.

8. The Early Effect is also called as
a) Base-width modulation effect
b) Base-width amplification effect
c) Both of the mentioned
d) None of the mentioned

View Answer

Answer: a [Reason:] At a given value of vBE, increasing vCE increases the reverse-bias voltage on the collector–base junction, and thus increases the width of the depletion region of this junction. This in turn results in a decrease in the effective base width W. Also the saturation current is inversely proportional to the width, the saturation current will increase and also makes collector current increases proportionally. This is the Early Effect. For the reasons mentioned above, it is also known as the base-width modulation effect.

9. For the BJT to operate in active mode Collector-Base junction must be
a) Heavily doped
b) Must reversed bias
c) Must be forward bias
d) Lightly doped

View Answer

Answer: b [Reason:] The BJT operates in active mode when the collector-Base junction is reversed bias. Also doping cannot prevent saturation of the transistor.

10. Collector current (Ic) reaches zero when
a) Vce = Vt ln (Isc/I)
b) Vt = Vce ln (Isc/I)
c) Vce = Vt ln (I/Isc)
d) Vce = Vt ln (Isc + I/I)

View Answer

Answer: a [Reason:] Ic = Is exp (Vbe/Vt) – Isc exp(Vbc/Vt). In this expression put ic = 0 and simplify.

Set 5

1. Which of the following is not a part of a BJT?
a) Base
b) Collector
c) Emitter
d) None of the mentioned

View Answer

Answer: d [Reason:] BJT consists of three semiconductor regions, base region, emitter region and collector region.

2. The number of pn junctions in a BJT is/are
a) 1
b) 2
c) 3
d) 4

View Answer

Answer: b [Reason:] There are two pn junctions, base-emitter junction and collector-emitter junction respectively.

3. In which of the following modes can a BJT be used?
a) Cut-off mode
b) Active mode
c) Saturation mode
d) All of the mentioned

View Answer

Answer: d [Reason:] These three are the defined regions in which a BJT operates.

4. If a BJT is to be used as an amplifier, then it must operate in___________
a) Cut-off mode
b) Active mode
c) Saturation mode
d) All of the mentioned

View Answer

Answer: b [Reason:] A BJT operates as an amplifiers in active mode and as a switch in cut-off or saturation mode.

5. If a BJT is to be used as a switch, it must operate in____________
a) Cut-off mode or active mode
b) Active Mode or saturation mode
c) Cut-off mode or saturation mode
d) Cut-off mode or saturation mode or active mode

View Answer

Answer: c [Reason:] A BJT operates as an amplifiers in active mode and as a switch in cut-off or saturation mode.

6. In cut off mode
a) The base-emitter junction is forward biased and emitter-collector junction is reversed biased
b) The base-emitter junction is forward biased and emitter-collector junction is forward biased
c) The base-emitter junction is reversed biased and emitter-collector junction is reversed biased
d) The base-emitter junction is reversed biased and emitter-collector junction is forward biased

View Answer

Answer: c [Reason:] In cut-off mode there is no current flowing through the BJT hence both junctions must be reversed biased else if either of them is forward biased then the current will flow.

7. On which of the following does the scale current not depends upon?
a) Effective width of the base
b) Charge of an electron
c) Electron diffusivity
d) Volume of the base-emitter junction

View Answer

Answer: d [Reason:] The saturation current does not depends upon the volume of the base-emitter junction. Instead it depends upon the area of the cross section of the base-emitter junction in a direction perpendicular to the flow of current.

8. On which of the following does the collector current not depends upon?
a) Saturation current
b) Thermal voltage
c) Voltage difference between the base and emitter
d) None of the mentioned

View Answer

Answer: d [Reason:] Collector current depends linearly of the saturation current and exponentially to the ratio of the voltage difference between the base and collector and thermal voltage.

9. The range for the transistor parameter also referred as common-emitter current gain has a value of__________ for common devices.
a) 50-200
b) 400-600
c) 750-1000
d) > 1000

View Answer

Answer: a [Reason:] Most commonly used transistors have a voltage gain of in the range of 50-200. Only some specially designed transistors have a transistor parameter in the range of 1000.

10. The collector current Ic is related to the emitter current Ie by a factor k. If b is the transistor parameter then the value of k in terms of b is
a) k = b/(b + 1)
b) k = (b + 1)/b
c) b = (k + 1)/k
d) None of the mentioned

View Answer

Answer: a [Reason:] Ic = k Ie (given) and also Ie = (b + 1)/b Ic (standard result). Equating these two results we get k = b/(b + 1).

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