Electric Drives Questions and Answers – Solid-State Devices – Transistors

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This set of Electric Drives Multiple Choice Questions & Answers (MCQs) focuses on “Solid-State Devices – Transistors”.

1. The base of a transistor is lightly doped.
a) True
b) False
View Answer

Answer: a
Explanation: The base of a transistor is lightly doped because it carries the electrons from the emitter and passed it to the collector region. There should be less recombination in the base region.
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2. Who is larger in size?
a) Base
b) Collector
c) Emitter
d) P-N Junction
View Answer

Answer: a
Explanation: Collector is larger in size because it receives the electrons from the base region. If it is not bigger in sizer there will be crowding of electrons which causes high power dissipation.

3. Calculate the collector current using the data: IE=14 mA, IB=7 mA.
a) 7 mA
b) 8 mA
c) 9 mA
d) 10 mA
View Answer

Answer: a
Explanation: The collector current in the transistor is IE-IB=14-7=7 mA. The KCL equation IE=IB+Ic is always in every configuration of the transistor.

4. Calculate the current gain using the data: Ic=25 mA, IB=10 mA.
a) 3.5
b) 2.5
c) 1.4
d) 7.8
View Answer

Answer: b
Explanation: The current gain is represented as β in electronic circuits. The current gain is the ratio of the collector current and base current. β=Ic÷IB=25÷10=2.5.

5. Calculate the value of ∝ using the data: Ic=18 mA, IE=17 mA.
a) 1.05
b) 1.47
c) 1.89
d) 2.55
View Answer

Answer: a
Explanation: The value of ∝ is Ic÷IE. The current gain is the ratio of the collector current and base current. ∝=Ic÷IE=18÷17=1.05.
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6. In a transistor, Ic=47 mA and IE=53 mA. The value of β is _____________
a) 8.48
b) 7.83
c) 9.26
d) 3.15
View Answer

Answer: b
Explanation: The value of β is Ic÷IB. The value of IB=IE-Ic=53-47=6 mA. The value of β is Ic÷IB=47÷6=7.83.

7. Choose the correct relationship between β and ∝.
a) β=∝/(1-∝)
b) β=1/(1+∝)
c) β=1/(1-∝)
d) β=1/(∝)
View Answer

Answer: a
Explanation: The relationship between β and ∝ is β=∝/(1-∝). The current gain is the ratio of the collector current and base current. The value of β is Ic÷IB.

8. A Transistor is a current operated device.
a) True
b) False
View Answer

Answer: a
Explanation: Transistor is a current operated device. The value of collector current is α times of the emitter current. It is a current controlled device.

9. Calculate the value of β for α=.8.
a) 2
b) 8
c) 3
d) 4
View Answer

Answer: d
Explanation: The relationship between β and ∝ is β=∝/(1-∝)=.8÷.2=4. The current gain is the ratio of the collector current and base current. The value of β is Ic÷IB.

10. Which one of the following is correct?
a) IE=IB+Ic
b) IE=IB-Ic
c) IE=Ic
d) IE=IB
View Answer

Answer: a
Explanation: The KCL equation that holds correct is IE=IB+Ic. At any point emitter current is the sum of the base current and collector current.
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11. In a transistor, IB=2 mA and Ic=3 mA. The value of β is _____________
a) 1.5
b) 5.8
c) 9.6
d) 3.5
View Answer

Answer: a
Explanation: The value of β is Ic÷IB. The value of IB and Ic are 2 mA, 3 mA. The value of β is Ic÷IB=3÷2=1.5.

12. In a transistor, β=75 and Ic=53 mA. The value of IB is _____________
a) .70 mA
b) .25 mA
c) .26 mA
d) .15 mA
View Answer

Answer: a
Explanation: The value of β is Ic÷IB. The value of IB=IE-Ic. The value of IB is Ic÷β=53÷75=.70 mA. The relationship between β and ∝ is β=∝/(1-∝).

13. Calculate the value of Vpeak if crest factor=5 and Vr.m.s=4 V.
a) 20 V
b) 30 V
c) 40 V
d) 50 V
View Answer

Answer: a
Explanation: The value of the crest factor is Vpeak÷Vr.m.s. The value of Vpeak is (crest factor) × Vr.m.s=5×4=20 V. It signifies the ratio of Vpeak and Vr.m.s.

14. Calculate the value of α for β=.2.
a) .85
b) .15
c) .23
d) .16
View Answer

Answer: d
Explanation: The relationship between β and ∝ is ∝=β/(1+β)=.2÷1.2=.16. The current gain is the ratio of the collector current and base current. The value of α is Ic÷IE.

15. Calculate the work done in stretching the wire of volume=12 m3 and the values of stress and strain are 28 N/m2 and 7.
a) 1176 J
b) 1544 J
c) 2542 J
d) 8788 J
View Answer

Answer: a
Explanation: The work done in stretching a wire is .5×Stress×Strain×Volume. The value of the work done is .5×12×28×7=1176 J.
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16. Calculate the compensator rating required for cos(Φ)=.35.
a) .936 P.U
b) .154 P.U
c) .481 P.U
d) .289 P.U
View Answer

Answer: a
Explanation: The compensator rating can be calculated using the relation QP.U=√1-cos2(∅)=√1-.1225=.936. This per unit value VAR compensator is required to improve the power factor of the system.

Sanfoundry Global Education & Learning Series – Electric Drives.

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn