Multiple choice

The input resistance Ri of the amplifier shown in the figure is

  1. $\dfrac{30}{4}K\Omega$
  2. 10 k$\Omega$
  3. 40 k$\Omega$

  4. infinite
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Since the inverting terminal is at virtual ground, the current flowing through the voltage source is $$ I_s = \dfrac{V_s}{10K} \\ or \quad \dfrac{V_s}{I_s} = 10 \ K\Omega = R_{in} $$

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