The virtual ground concept in op-amp is valid for negative feedback.

Explanation:
Op-amp stands for operational amplifier, which is an electronic device that amplifies the difference between two input voltages and produces an output voltage. The virtual ground concept is a fundamental principle in op-amp circuits and is primarily applicable in the case of negative feedback.

What is the virtual ground concept?
In an ideal op-amp, the input impedance is infinite and the input current is zero. This means that no current flows into the input terminals of the op-amp. When negative feedback is applied to an op-amp circuit, the output voltage adjusts in such a way that the voltage at the inverting (-) input terminal becomes equal to the voltage at the non-inverting (+) input terminal. This phenomenon is known as the virtual ground concept.

Why is the virtual ground concept valid for negative feedback?
Negative feedback is a technique used in op-amp circuits to stabilize and control the output voltage. In a circuit with negative feedback, a portion of the output voltage is fed back to the inverting input terminal. This feedback voltage is compared to the input voltage at the non-inverting input terminal, and the op-amp adjusts its output voltage to minimize the difference between these two voltages.

Implications of the virtual ground concept in negative feedback:
1. Zero voltage difference: In an op-amp circuit with negative feedback, the virtual ground concept ensures that the voltage at the inverting input terminal is virtually equal to the voltage at the non-inverting input terminal. This implies that the voltage difference between these two terminals is effectively zero.

2. Input impedance: The virtual ground concept also implies that the inverting input terminal is at ground potential (zero volts) due to the negative feedback. This results in a high input impedance, as no current flows into the inverting input terminal.

3. Summing point: The virtual ground concept allows multiple input signals to be summed at the inverting input terminal. This is often used in op-amp circuits for applications such as amplification, signal conditioning, and filtering.

4. Linear operation: The virtual ground concept ensures linear operation of the op-amp in the negative feedback configuration. By maintaining the inverting input terminal at virtual ground, the op-amp operates in its linear region, providing accurate and predictable amplification.

In summary, the virtual ground concept is valid for op-amp circuits with negative feedback. It ensures that the inverting input terminal is maintained at the same voltage as the non-inverting input terminal, resulting in a variety of benefits such as high input impedance, summing capabilities, and linear operation.