Description

An effect found on the inverting input of operational amplifiers, which causes the measured potential difference to drop to zero Volts.

Cause and Effect

This property remains true for any voltage applied to the -ve input of an inverting Op-Amp (within its linear range). Beacuse they are current-triggered devices, and not voltage-triggered, Op-Amps do not produce a voltage drop. This is due to the high impedance on their inputs, and negative feedback.

Further Explanation

Operational amplifiers are analog electronic devices originally built for analog computation. They have two inputs (inverting and non-inverting), and one output. Their most common use in modern electronics is amplification. This is accomplished by feeding the output current into one of the inputs of the device, thus creating a feedback loop. Normally, one would expect there to be a voltage drop on any electrical component, proved using Ohm's Law (V=IR). But, what if there is no current flow?.

On an inverting amplifier (when the inverting input is used for feedback), current flowing into the input gathers at the input pin because of its high impedance (net resistance). This causes the output pin to go negative to such a degree that the current pulled though the feedback line equals that at on the input line.

Think of a T-junction, and all the cars are travelling in one direction, taking one of the two roads available only. The cars are coming from your current source, and are driving towards the feedback line. The reason for this is the great big wall stuck in the middle of the other road.

This 'other road' is the input pin of the Op-Amp, and with no current, V=0*R=0 (zero Volts).

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