Op-amp polarity with inverting input drive — clarification: If an input signal is applied to the inverting (−) input of an operational amplifier while the noninverting (+) input is tied to ground (0 V reference), the closed-loop output (with standard negative feedback) will be opposite in polarity (inverted) relative to the input signal. Is this statement correct?

Introduction / Context:
Operational amplifiers (op-amps) are the core of countless analog circuits. One of the first concepts learners meet is the polarity behavior of inverting versus noninverting configurations. This question asks whether driving the inverting input while grounding the noninverting input produces an output that is opposite in polarity to the input. Understanding this sign inversion is essential for signal conditioning, sensor interfaces, and control systems.

Given Data / Assumptions:

• The inverting (−) input is driven by a source through an input network.
• The noninverting (+) input is at 0 V (signal ground).
• Standard negative feedback is present to set the closed-loop gain.
• Ideal op-amp assumptions: very high open-loop gain, infinite input impedance, and zero output impedance for conceptual analysis.

Concept / Approach:
In the classic inverting amplifier, negative feedback forces the op-amp to hold the differential input near zero (the “virtual short” concept). Since the noninverting input is at 0 V, the inverting input node sits at a “virtual ground.” The output must move in whatever direction is necessary to reduce the input difference to nearly zero. Because the input signal is applied to the inverting input, the output moves in the opposite direction to cancel the error, producing inversion.

Step-by-Step Solution:

Verification / Alternative check:
For an inverting stage, closed-loop gain is Av = −Rf/Rin. The negative sign explicitly denotes inversion. Lab measurements confirm that a sine wave at the input emerges inverted at the output when the (+) input is grounded and negative feedback is used.

Why Other Options Are Wrong:

• Incorrect: Conflicts with the defining property of the inverting configuration.
• Only true for DC signals: Inversion holds for AC and DC within bandwidth limits.
• Only true when open-loop: Open-loop operation is not stable for linear amplification; inversion is a closed-loop attribute here.

Common Pitfalls:
Confusing the inverting topology with noninverting; overlooking that the inversion result depends on negative feedback, not on operating the device open-loop.

Final Answer:
Correct