If one input of an operational amplifier is grounded while a signal is applied to the other input, what mode or configuration is the op-amp said to be operating in?

Introduction:
Op-amps can be driven in different ways depending on whether one or both inputs carry a signal. Understanding single-ended versus differential (double-ended) stimulation is key to interpreting gain, noise, and common-mode behavior. This question identifies the correct descriptor when one input is grounded and the other receives the signal.

Given Data / Assumptions:

• Two-input op-amp (inverting and noninverting terminals).
• One input explicitly connected to ground (0 V reference).
• Other input receives the signal, possibly through a network.

Concept / Approach:
When only one input is driven and the other is at ground, the amplifier is being driven single-ended. If both inputs receive equal and opposite signals, it is double-ended (fully differential). “Common-mode” refers to identical signals at both inputs, not one grounded and one driven. “Noninverting mode” is a particular single-ended topology but requires clarifying which terminal is driven and feedback arrangement; the question asks more generally about the drive type, not the specific feedback configuration.

Step-by-Step Solution:

Verification / Alternative check:
In instrumentation amplifiers, double-ended (fully differential) drive improves CMRR; by contrast, the described setup is clearly single-ended, confirming the terminology.

Why Other Options Are Wrong:

• Common-mode: Requires identical signals on both inputs.
• Double-ended: Needs both inputs driven with signals.
• Noninverting mode: Possible only if the + input is driven and feedback is configured appropriately; the question does not assert that specific topology.

Common Pitfalls:
Equating “one input grounded” with a specific polarity (inverting vs noninverting); forgetting that “mode” can refer to drive type (single vs double-ended) or feedback topology (inverting/noninverting) depending on context.

Final Answer:
Single-ended.