Analog Circuits Questions and Answers Part-18

1. Attenuators are active devices.
a) True
b) False

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.

2. 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 tunneling effect

Answer: a
Explanation: It is an active device since its impedance is positive and the V-I characteristics lie in the 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.

3. The unit of gain is ________
a) Joules
b) Decibels
c) Its unit less
d) Watts

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.

4. Reverse saturation current of a common emitter transistor is __________
a) Collector current when emitter is open circuited and base-collector junction is reverse biased
b) Emitter current when collector is open circuited and base-collector junction is reverse biased
c) Base current when emitter circuit is open circuited and emitter-collector junction is reverse biased
d) Collector current when base circuit is open circuited

Answer: a
Explanation: Reverse saturation current is the collector current when emitter is open circuited and base-collector junction is reverse bias mode. In this mode of operation collector-base junction act as a reverse biased diode. The current in this reverse biased junction is known as reverse saturation current.

5. Reverse collector saturation current ICBO is __________
a) Collector current when emitter current is zero
b) Collector current when base current is zero
c) Same as reverse saturation current
d) Collector current when either emitter or base current is zero

Answer: a
Explanation: Reverse collector current ICBO is collector-base current when emitter is open. This is same as reverse saturation current in ideal but have slight difference in practical

6. Reverse collector saturation is greater than Reverse saturation current because of reverse collector saturation __________
a) Is ideal
b) Doesn’t include leakage current
c) They are same
d) Include avalanche multiplication current which is caused by the collision in collector junction

Answer: d
Explanation: One of the reasons why reverse collector current exceeds the reverse saturation current is the introduction of avalanche multiplication current in the base collector junction. This happens when high energy electron collides in the lattice it creates more number of electron and thus a greater current. Another major reason is the presence of surface leakage currents flowing in the reverse collector saturation.

7. Reverse collector saturation is greater than Reverse saturation current because reverse collector saturation __________
a) Is ideal
b) Consist leakage current flowing through junction and surface
c) Doesn’t include avalanche multiplication current opposing collector current
d) They are same

Answer: b
Explanation: One of the reasons why reverse collector current exceeds the reverse saturation current is the introduction of avalanche multiplication current in the base collector junction. This happens when high energy electron collides in the lattice it creates more number of electron and thus a greater current. Another major reason is the presence of surface leakage currents flowing in the reverse collector saturation.

8. Which of the following statement about a common base transistor is true?
a) Very low input impedance
b) Very low output Impedance
c) Current gain is greater than unity
d) Voltage gain is very low

Answer: a
Explanation: Common base transistor has very low input resistance (20Ω). It also has very high output resistance. Its current gain is less than unity and it has a medium voltage gain.

9. Which of the following statement about a common emitter transistor is true?
a) Very high input resistance
b) High output resistance
c) Current gain is less than unity
d) Voltage gain is very low

Answer: b
Explanation: Common emitter transistor has high output resistance (about 40k). It has low input resistance (about 1k). Current gain is high (20 to a few hundred). Voltage gain is medium.

10. Which of the following statement about a common collector transistor is true?
a) Very low input impedance
b) Very high output impedance
c) Unity current gain
d) Unity voltage gain

Answer: d
Explanation: Common collector configuration has high input impedance and low output impedance. The current gain is high but voltage gain is low, almost equal to unity.