# Mechatronics Questions and Answers – Solid State Electronic Devices – Bipolar Junction Transistors

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This set of Mechatronics Multiple Choice Questions & Answers (MCQs) focuses on “Solid State Electronic Devices – Bipolar Junction Transistors”.

1. A bipolar junction transistor has beta=250 and base current=10micro ampere. What is the collector current?
a) 25 micro ampere
b) 10 micro ampere
c) 2.5 milli ampere
d) 10 milli ampere

Explanation: Given:
Base current(Ib)=10micro ampere
Beta=250
Since Ic(collector current)=beta*Ib(base current)
Ic(collector current)=250*10 micro ampere=2.5 milli ampere.

2. What happens to the collector current if the emitter current increases while no base voltage is applied?
a) Increases
b) Decreases
c) No current
d) First increases then decreases

Explanation: When no voltage is provided at the base then no current passes from emitter to collector, so even if very high potential difference is applied at the emitter collector junction, no current flows through it. This configuration is used for switching in various appliances using bipolar junction transistor.

3. Which terminal of the diode is common to the other two terminals of the diode?
a) Base is common to collector and emitter
b) Emitter is common to collector and base
c) Collector is common to base and emitter
d) No terminal is common to any other

Explanation: Base terminal is common to collector and emitter terminal of the diode. A bipolar junction transistor is made by sandwiching base terminal between emitter and collector terminal. If base terminal is made of N type material then both emitter and collector terminal is made of P-type material and vice-versa.
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4. Which is an example of bipolar junction transistor?
a) BC547B
b) CMCP793V-500
c) SLB700A/06VA
d) MBR5H100MFST1G

Explanation: BC547B is an example of bipolar junction transistor. It is most common and widely used NPN transistor. It is small, cheap, uses less power and fulfills most of the requirement for general purpose use.

5. In bipolar junction transistors both electron and holes are responsible for conduction.
a) True
b) False

Explanation: In bipolar junction transistors both electron and holes are responsible for conduction. The term “bipolar” itself mean two polarities which represents that both charged particle are responsible for the conduction in the bipolar junction transistor.

6. Three PN junctions is present in a bipolar junction transistor.
a) True
b) False

Explanation: A bipolar junction transistor has 2 PN junctions. First PN junction is between the base emitter terminal and second PN junction is between base collector terminal. A base is always between emitter and collector.

7. What is the minimum voltage required to make base emitter junction of a real silicon bipolar junction transistor in forward biased?
a) 0.7 volts
b) 1.8 volts
c) 2.3 volts
d) 0.3 volts

Explanation: 0.7 volts is the minimum voltage required to make the base emitter junction of a real silicon bipolar junction transistor in forward biased. This 0.7 volt potential difference between base and emitter terminal makes the PN junction in forward biased.

8. When bipolar junction transistor acts as an amplifier?
a) When base emitter terminal is forward biased and base collector terminal is reverse bias
b) When base emitter terminal is reverse biased and base collector terminal is reverse bias
c) When base emitter terminal is reverse biased and base collector terminal is forward bias
d) When base emitter terminal is forward biased and base collector terminal is forward bias

Explanation: Bipolar junction transistor acts as an amplifier when base emitter terminal is forward biased and base collector terminal is reverse biased. There is a transfer of resistance from low resistance to high resistance while the current remains same, and since V=IR, the voltage gets amplified.

9. What are the parameters over which transfer characteristics curve of bipolar junction transistor is made in common emitter configuration?
a) Emitter Current and time
b) Emitter Voltage and time
c) Collector Current and frequency
d) Collector to Emitter Voltage and Collector current

Explanation: Collector to Emitter Voltage and Collector current are the parameters considering which transfer characteristics curve of bipolar junction transistor is made. It is voltage versus current graph in which Current is denoted on Y-axis and voltage is denoted on (X-axis).

10. What are the parameters over which Input characteristics curve of bipolar junction transistor is made in common emitter configuration?
a) Emitter Current and time
b) Emitter to base Voltage and time
c) Collector Current and frequency
d) Base to Emitter Voltage and base current

Explanation: Base to Emitter Voltage and base current are the parameters considering which input characteristics curve of bipolar junction transistor is made. It is voltage versus current graph in which Current is denoted on Y-axis and voltage is denoted on (X-axis).

11. A bipolar junction transistor has beta=100 and base current= 8 micro ampere. What is the collector current?
a) 25 micro ampere
b) 0.8 micro ampere
c) 0.8 milli ampere
d) 10 milli ampere

Explanation: Given;
Base current (Ib) = 8 micro ampere
Beta=100
Since Ic(collector current)=beta*Ib(base current)
Ic(collector current)=100*8 micro ampere=0.8 milli ampere.

12. A bipolar junction transistor has collector current(Ic)=1.3 milli ampere and emitter current=1.5 milli ampere. What is the base current?
a) 25 micro ampere
b) 0.2 micro ampere
c) 0.2 milli ampere
d) 10 milli ampere

Explanation: Given;
Collector current (Ic)=1.3 milli ampere
Emitter current (Ie)=1.5 milli ampere
Since Ie(emitter current)=Ic(collector current)+Ib(base current)
Therefore Ib(base current)=Ie(emitter current)-Ic(collector current).
Ib(base current)=1.5 mA-1.3 => 0.2 milli ampere

13. A bipolar junction transistor has emitter current(Ic)=1.6 milli ampere and collector current=1.47 milli ampere. What is the base current?
a) 25 micro ampere
b) 0.13 microampere
c) 0.8 milli ampere
d) 0.13 milli ampere

Explanation: Given:
Collector current(Ic)=1.47 milli ampere
Emitter current(Ie)=1.6 milli ampere
Since Ie(emitter current)=Ic(collector current)+Ib(base current)
Therefore Ib(base current)=Ie(emitter current)-Ic(collector current).
Ib(base current)=1.6-1.47 => 0.13 milli ampere

14. What is the value of current gain (α) where emitter current(Ic)=1.6 milli ampere; collector current=1.5 milli ampere and base current=0.1 milli ampere?
a) 3.1
b) 0.937
c) 0.8
d) 0.31

Explanation: Given:
Collector current(Ic)=1.5 milli ampere
Emitter current(Ie)=1.6 milli ampere
Base current=0.1 milli ampere
Since: current gain( α )=Ic(collector current)/Ie(emitter current)
Therefore current gain(α)=1.5/1.6 => 0.937

15. What is the value of current gain (α) where emitter current(Ic)=2 milli ampere; collector current=1.9 milli ampere and base current=0.1 milli ampere?
a) 1.5
b) 0.937
c) 80
d) 150

Explanation: Given:
Collector current(Ic)=1.59 milli ampere
Emitter current(Ie)=1.6 milli ampere
Base current=0.01milliampere
Since: Voltage gain( β )=Ic(collector current)/Ib(base current)
Therefore; Voltage gain( β )=1.5/0.01 => 150

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