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Online MCQ Assignment
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1. The frequency of Colpitts oscillator is expressed as
(Where L is inductance and C is the effective capacitance)
a) 1/(4ᴨ√LC)
b) 1/(2ᴨ√LC)
c) 1/(3ᴨ√LC)
d) √3/(2ᴨ√LC)

Answer: b [Reason:] The frequency of colpitts oscillator is expressed as 1/(2ᴨ√LC) where L is inductance and C is effective capacitance.

2. Colpitts oscillator uses which type of feedback
a) Negative feedback
b) Positive feedback
c) No feedback
d) Positive or Negative depends upon frequency

Answer: b [Reason:] Colpitts oscillator as normal oscillator uses positive feedback for oscillation to satisfy Barkhausen’s criteria.

3. To ensure constant feedback which method is used in Colpitts oscillator
a) Gang tuning
b) Using same capacitor
c) No method is used
d) Voltage divider always gives constant feedback

Answer: a [Reason:] To ensure constant feedback gang tuning is used in Colpitts oscillator.

4. If C1 and C2 are the capacitance used in Colpitts oscillator the effective capacitance in the equation of frequency calculation is equal to
a) (ᴨ×C1×C2)/(C1+C2)
b) 3 (C1×C2)/(C1+C2)
c) (C1×C2)/(2ᴨ(C1+C2))
d) (C1×C2)/(C1+C2)

Answer: d [Reason:] In the tank circuit of Colpitts oscillator there are two capacitors connected in series and hence effective capacitance is (C1×C2)/(C1+C2).

5. Which configuration of transistor amplifier is used for Colpitts oscillator?
a) Common emitter amplifier
b) Common collector amplifier
c) Common base amplifier
d) Combination of both common emitter and common collector

Answer: a [Reason:] Common emitter configuration is used for amplifying distorted oscillatory signal to a perfect oscillation.

6. Phase shift provided by overall tank circuit is
a) 0 degree
b) 90 degree
c) 180 degree
d) -90 degree

Answer: c [Reason:] The overall phase shift provided by tank circuit is 180 degrees. Since active element produces a phase shift of 180 degrees the tank circuit should create 180 degrees to obey Barkhausen’s criteria.

7. The gain device in the colpitts oscillator act as a
a) Low pass filter
b) High pass filter
c) Band pass filter
d) Band rejection filter

Answer: c [Reason:] The gain device in Colpitts oscillator act as a band pass filter and thus limits frequency of oscillation to a certain range.

8. Which of the following equation gives amplitude of oscillation in Colpitts oscillator using describing function method? (Where Ic is the is the bias current RL is the load resistor and C1 & C2 are the upper and lower capacitance of voltage divider bias)
a) 2ICRL/C1+C2
b) 2ICC2/C1+C2
c) 2ICRL C2/C1
d) 2ICRL C2/C1+C2

Answer: d [Reason:] Amplitude of oscillation in Colpitts oscillator using describing function method is egual to V=(2IC RL C2)/C1.

9. The improvement of Colpitts oscillator over Hately oscillator is, Colpitts oscillator’s performance in
a) All frequency region
b) Mid frequency region
c) High frequency region
d) Low frequency region