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5. Describe an amplifier in which the whole of the output signal is fed back in opposition to the input signal. Deduce the gain of this amplifier with feedback and suggest an application for the amplifier.
(a) Describe an operational amplifier with negative feedback and derive an expression for the voltage gain in terms of the feedback components.
(b) An amplifier with a voltage gain of -20,000 is used in a feedback circuit where
β = 0.02. Calculate the overall gain with feedback. If the gain of the amplifier dropped to one-half of its inherent value because of a reduction in the supply voltage, what would the overall circuit gain become?

Answer:
(b) The relation among open-loop gain AOL, closed-loop gain ACL and feedback factor βis:
ACL=AOL/（1+β*AOL）
   So: ACL=AOL/（1+β*AOL）
                    =20000/（1+0.02*20000）
                    =49.88
 
When the amplifier gain was reduced to half of its original:
  ACL=AOL/（1+β*AOL）
                    =10000/（1+0.02*10000）
                    =49.75

6. Draw and describe an oscillator using a single transistor stage as an amplifier, with feedback applied by the way of an LC circuit. How could the feedback fraction be adjusted in an oscillator of this sort?
[Hint:- A single stage collector emitter amplifier having a resistive load replaced by an LC https://www.51lunwen.org/computer/ tuned circuit is basically referred to as a tuned-collector oscillator]

Answer: 
If parallel LC network as amplifying circuit of the collector load, then the circuit's voltage will gain. Shown in Fig. 6-1
          
According to the frequency characteristics of LC parallel network, when f = f0, the voltage gain maximum values, and no additional phase shift. For the rest of the signal frequency, voltage gain value not only reduced, but also has an additional phase shift. Circuit has a characteristic of selective frequency, so it is called selective frequency amplifier. If we can introduce of positive feedback in the circuit, and the feedback voltage can be used to replace the input voltage, the circuit becomes sine wave oscillator circuit. 
             Fig. 6-1

7. Draw and describe an the operation of a single stage transistor oscillator using C and R elements in its feedback network and discuss any advantages and disadvantages this circuit might have.

Answer:
1. Advantages: RC Sinusoidal Oscillation Circuit treat RC series-parallel network as selected frequency network and positive feedback network. The oscillation frequency is stability, its load capacity is strong and the output voltage distortion is small, etc. Therefore, it has a wide range of applications.
2. Disadvantages: RC oscillator frequency cannot be too high
 

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