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These are the correct answers

1. Answer: a
Explanation: Voltage series feedback is used in Colpitts oscillator. In voltage series feedback a part of output voltage is fed back to input.
2. Answer: a
Explanation: A capacitor with a center tap or simply two capacitors in parallel to an inductor, acting as a voltage divider, act as the feedback system, providing feedback to the base of the amplifying transistor. Oscillations across the capacitor are applied at the base-emitter junction and appear across the collector as an amplified output.
3. Answer: d
Explanation: Capacitive voltage divider network is used for giving positive feedback in Colpitts oscillator. Oscillations across the capacitor are applied at the base-emitter junction and appear across the collector as an amplified output. The amount of feedback depends on the ratio of the two capacitors being used.
4. Answer: b
Explanation: There are two capacitors in the tank circuit of Colpitts oscillator and it is given for voltage division.
5. Answer: a
Explanation: There are one inductor in the tank circuit of Colpitts oscillator and it is given for oscillation.
6. Answer: b
Explanation: Capacitive circuit in the colpitt oscillator improves frequency stability. An additional 180° phase shift is provided by the capacitive tank circuit, providing no phase shift to the output. By changing tap position or the value of capacitors in the tank circuit, we can change feedback amount.
7. Answer: d
Explanation: The active element used in Colpitts oscillator is transistor and it is used for amplification of weak oscillator signals.
8. Answer: a
Explanation: RFC choke present in Colpitts oscillator is to provide high reactance to AC oscillation and low reactance to DC supply to improve performance.
9. Answer: c
Explanation: RFC choke present in Colpitts oscillator is to provide high reactance to AC oscillation and low reactance to DC supply to improve performance. If resistor is used there will be some power loss in DC biasing which is unnecessary.
10. Answer: b
Explanation: Resistors are used to bias transistor to its DC operating point. Capacitor divider circuit provides input bias to the amplifying element.