Ground concepts in op-amp analysis: Current cannot physically flow into a node that is only a “virtual ground.” Which term correctly completes the statement “Current cannot flow to ground through a(n) _____” ?

Introduction / Context:
Ground terminology causes confusion. In op-amp circuits, a “virtual ground” refers to a node that is held at (or near) ground potential by feedback, but is not a physical connection to the ground reference. Understanding this helps avoid incorrect assumptions about current paths.

Given Data / Assumptions:

• Ideal op-amp enforcing v(+) ≈ v(−) under negative feedback.
• “Virtual ground” is a potential condition, not a conductive path.
• Other listed grounds are actual low-impedance references under stated conditions.

Concept / Approach:
A mechanical (chassis) ground and an AC ground (node held at AC zero by a capacitor or low impedance) provide conductive paths for current at least over some frequency range. A virtual ground only has the same voltage as ground but is not physically connected to the ground node; feedback adjusts the op-amp output to keep the potential near zero. Therefore, no current can flow “to ground” through a virtual ground merely by virtue of its name.

Step-by-Step Solution:

Verification / Alternative check:
In an inverting amplifier, the summing junction is at ~0 V (virtual ground), yet input current flows through Rin into the junction and then through the feedback network to the op-amp output, not into ground.

Why Other Options Are Wrong:
Mechanical ground: chassis conductive metal can carry current.
AC ground: low impedance for AC lets current flow for those frequencies.
Virtual short: refers to v(+) ≈ v(−); says nothing about ground path.

Common Pitfalls:
Assuming “virtual ground” equals a wired ground; forgetting that a measurement referenced to true ground may see small error at the virtual node due to finite loop gain.

Final Answer:
virtual ground