Question

For an Op-amp (operational amplifier) with negative feedback, the output is:
A. equal to the output
B. increased
C. feedback for the inverting input
D. feedback to the non-inverting input

Answer 1

Hint: Negative feedback refers to providing feedback to the inverting input terminal. There are two types of circuits for an Op-Amp. Inverting and non-inverting circuit. The negative feedback (feedback to inverting terminal) is applied for the inverting circuit.

Complete answer:
The operational amplifier shortly known as Op-Amp is a voltage amplifier. For the operation of Op-Amp, a feedback resistor is used for the monitoring of the output. In other words, a feedback connection is used for tracking the operation of Op-Amp. An Op-Amp IC is named IC741 which is an 8 pin IC.

Basic symbolic representation:

Internally both inverting and non-inverting terminals are connected by a resistance. For ideal cases the value of this resistance is infinity. +Vcc and –Vcc are the supply terminals for Op-Amp. The inverting terminal inverts any coming signal by an angle of \[180{}^\circ \]. When we need a signal the same as the input signal the system is connected by a non-inverting terminal.

The internal structure of an Op-Amp is very complex. A simplified version of Op-Amp is shown here :

                

Ri is the internal resistance between two input terminals. Ro is the output resistance of the Op-Amp. G represents the gain of the amplifier which is different for both (inverting and non-inverting) the cases.

The inverting amplifier configuration is shown below:

An inverting amplifier is taken into account when we want to output with $180{}^\circ $ phase shift. For this, feedback is applied to the inverting terminal of the Op-Amp and the non-inverting terminal is grounded.

So, the correct answer is “Option C”.

Note:
The feedback is applied to the inverting terminal for negative feedback and feedback is applied to the non-inverting terminal when 0 phase variation is required. For ideal situations, Ri is equivalent to infinity so that no current flows through the inverting and non-inverting terminal, and Ro is minimum so that maximum output can be obtained.