Question

The input resistance of the op-amp circuit shown is:

• A. \(100\ \text{k}\Omega\)
• B. \(1\ \text{k}\Omega\)
• C. \(99\ \text{k}\Omega\)
• D. \(101\ \text{k}\Omega\)

Hint:

In op-amp circuits, input resistance = external series resistance if connected to non-inverting terminal.

Answer 1

The Correct Option is B

To find the input resistance of the op-amp circuit, let's analyze the configuration. This is a non-inverting amplifier with an input resistor \(R_{\text{in}}\). In a non-inverting configuration, the input resistance (\(R_{\text{in}}\)) is primarily determined by the resistance connected directly to the input terminal. Typically, operational amplifiers are considered to have infinite input impedance, but the circuit's input resistance is determined by the connected components.
The input resistance \(R_{\text{input}}\) at the non-inverting terminal can be considered to be equal to the resistor connected to the input terminal, which is \(R_{\text{in}}\).
Given the options provided and knowing standard op-amp feedback configurations, for a non-inverting amplifier setup, the input impedance seen by the source is approximately equal to the resistor \(R_{\text{in}}\) due to the high impedance nature of op-amp inputs. Therefore, the input resistance \(R_{\text{input}} = 1\ \text{k}\Omega\), which matches the correct and expected value.
Conclusion: The input resistance of the given op-amp circuit is \(1\ \text{k}\Omega\).