Analog Circuits Questions and Answers – Active and Passive Devices

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This set of Analog Circuits Multiple Choice Questions & Answers (MCQs) focuses on “Active and Passive Devices”.

1. An active device is one which ___________
a) Mechanically controls electron flow
b) Electrically controls electron flow
c) Pneumatically controls electron flow
d) Automatically controls electron flow
View Answer

Answer: b
Explanation: An active device is any type of circuit component with the ability to electrically control electron flow (electricity controlling electricity). For a circuit to be properly called electronic, it must contain at least one active device.
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2. Which of the following elements comprise of the passive devices?
a) Resistors, Capacitors and SCRs
b) Vacuum Tubes, SCRs and Diodes
c) Transformers, Inductors and Diodes
d) Transformers, TRIACs and DIACs
View Answer

Answer: c
Explanation: A passive device is any type of circuit component which cannot control the flow of electrons by means of any electric control. All these devices do not have the ability to electrically control the flow of electrons.

3. A transistor is a current controlled device because_______________
a) In the base region movement of charge carrier is because of the electrons which are minority charge carrier in the base region
b) In the collector region movement of charge carrier is because of the electrons which are minority charge carrier in the collector region
c) In the base region movement of charge carrier is because of the holes which are majority charge carrier in the base region
d) In the collector region movement of charge carrier is because of the holes which are majority charge carrier in the base region
View Answer

Answer: a
Explanation: In the base region movement of charge carrier is because of the electrons which is minority charge carrier in the base region. So, a BJT can said to be minority current controlled device. Base current flows between base and emitter in the BJT to induce a larger current flow between emitter and collector.

4. Active devices can also be used as_________
a) Amplifiers
b) Choppers
c) Converters
d) Inverters
View Answer

Answer: a
Explanation: Active devices may be employed to a govern large amount of power by application of small amount of power. This behaviour is known as amplification. Therefore, active devices can be used as amplifiers.

5. How do amplifiers work without violating Law of Conservation of Energy?
a) They amplify one factor of the input and reduce others
b) They work on the law of conservation of mass
c) They violate the Law of Conservation of Energy
d) They amplify the signal by taking an input from an external source
View Answer

Answer: d
Explanation: The Law of Conservation of Energy is not violated because the additional power is supplied by an external source, usually a DC battery or equivalent. The amplifier neither creates nor destroys energy, but merely reshapes it into the waveform desired.
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6. The overall gain of multiple amplifiers in cascade can be expressed as__________ (A1, A2, A3 are individual gains)
a) A1-A2-A3
b) A1+A2+A3
c) A1/A2*A3
d) A1*A2*A3
View Answer

Answer: d
Explanation: Gain can be voltage, current or power. Thus, when we put multiple stages in cascade the total gain will be the product of gains at individual stages. This is because the gain in successive stages increases greatly because of multiplication.

7. To overcome the problem of representation of large values of gain, which of the following units was introduced?
a) Decibels
b) Joules
c) Pascals
d) Farads
View Answer

Answer: a
Explanation: Since 1dB=(1/10)log10(A2/A1) it is a logarithmic scale of representation and very large values can be expressed by smaller numbers. Decibels is a convenient unit of measurement for a variety of applications.

8. Attenuators are active devices.
a) True
b) False
View Answer

Answer: b
Explanation: Attenuators weaken or attenuate the high-level output of a signal generator and thus cannot control the signals electronically. This makes them passive devices and they can only be present in a circuit with an active device.

9. Tunnel diode can be used as an active device because__________
a) its negative resistance region is used
b) it conducts at a faster rate
c) it triggers the flow of electrons in reverse bias
d) of tunnelling effect
View Answer

Answer: a
Explanation: It is an active device since its impedance is positive and the V-I characteristics lie in first & second quadrants, tunnel diodes can be used as an active device even though it is a diode which falls under the category of passive devices.
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10. The unit of gain is________
a) Joules
b) Decibels
c) Its unit less
d) Watts
View Answer

Answer: c
Explanation: Gain is the ratio of same type of values i.e. either volt/volt or current(amp)/ current(amp) or watts/watts thus this makes it unit less. If it is expressed in decibels i.e. on a logarithmic scale, then they have the unit dB.

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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