Operational amplifier
Why amplifier:
electronic instrumentation system employs sensors that report their outputs as voltage. In some cases the output of a sensor may be only millivolts in amplitude. In order to see the sensor signal on an oscilloscope or convert it to digital form, the signal must be amplified. Sometimes the unstimulated sensor output is brought to zero by an offset circuit, such as a Wheatstone bridge for strain gauges. Again, in this case, an amplifier is called for.
You as the designer of the system likely want some control over the amplitude of the output, and therefore are motivated to learn about circuits that provide voltage gain; such circuits are called amplifiers.
The ideal amplifier
An ideal amplifier will pass the input signal through to the output undistorted but enlarged (gain set by user), with no delay. It will not be affected by the output impedance of the source (sensor). In addition the ideal amplifier will be able to drive any load: supply any current.
No real amplifier is ideal, but an op amp can come close, at least with regard to gain at low frequency. The typical IC op amp has an open loop gain of 10^6 and a low frequency input impedance of about 10^12 ohms. We ll see shortly how such high open loop gain is harnessed to create user-desired gains.
It use mostly in inverting amplifier inverting amplifier and non-inverting amplifier