What value of input resistance is needed in the given circuit to produce the given output voltage ?

F1 Shubham.B 19-01-21 Savita D21

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VSSC (ISRO) Technician B (Electronic Mechanic) Previous Year Paper (Held on 25 Sept 2016)
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  1. 50 Ω
  2. 4 kΩ
  3. 4.08 kΩ
  4. 5 kΩ

Answer (Detailed Solution Below)

Option 2 : 4 kΩ
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Detailed Solution

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Concept:

F1 S.B Madhu 10.07.20 D2

 

For an inverting amplifier, as shown above, the voltage gain is given by:

\(A_v=\frac{V_{out}}{V_{in}}\)

The ideal opamp will be having virtual ground and the current entering the op-amp will be 0.

Therefore, by applying KCL at the inverting terminal of opamp we get:

\(\frac{V_{in}-0}{R_1}=\frac{0-V_{out}}{R_f}\)

\(\frac{V_{out}}{V_{in}}=-\frac{R_f}{R_i}\)

Calculation:

\(\frac{V_{out}}{V_{in}}=-\frac{R_f}{R_i}\)

Ri = (60 × 10-3 × 200 × 103)/3

Ri = 4 kΩ 

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