If V1 and V2 are equal in value, Vo equals which expression?

If V1 and V2 are equal in value, Vo equals which expression?

• A. Vo = Va
• B. Vo = 2 Va
• C. Vo = 0
• D. Vo = -Va

Answer: (A)

When an op-amp has negative feedback, it adjusts its output so that the voltages at its two inputs become equal (a virtual short). If V1 and V2 end up being equal, the differential input is effectively zero, and the circuit settles with the inverting input matching the non-inverting input. Here, Va is the voltage at the non-inverting input. With V1 = V2, the feedback forces the inverting input to equal Va, and the output must take the value that makes that condition true. In this configuration, that means Vo equals Va. Thus, the output follows the input voltage at the non-inverting terminal, giving Vo = Va. The other expressions would require different gain or inversion that this circuit does not provide.

When an op-amp has negative feedback, it adjusts its output so that the voltages at its two inputs become equal (a virtual short). If V1 and V2 end up being equal, the differential input is effectively zero, and the circuit settles with the inverting input matching the non-inverting input.

Here, Va is the voltage at the non-inverting input. With V1 = V2, the feedback forces the inverting input to equal Va, and the output must take the value that makes that condition true. In this configuration, that means Vo equals Va.

Thus, the output follows the input voltage at the non-inverting terminal, giving Vo = Va. The other expressions would require different gain or inversion that this circuit does not provide.