This set of Electronic Devices and Circuits Multiple Choice Questions & Answers (MCQs) focuses on “BJTs Device Strucutres and Physical Operations”.
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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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
Explanation: 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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