Operational amplifiers (op amps) are components used to amplify
or other wise modify a voltage signal. They usually come
in the form of an integrated circuit chip. There are two inputs,
one negative and one positive, and one output. Op amps are
active components, that is they require a power supply to operate.
The power supply connections, however, are usually left out of circuit diagrams.
An isolated op amp has a very high gain. In other words, it multiplies the difference in voltage between its inputs by a very large number (a million or more) and presents it at the output. Op amps are, however, rarely used in this way. Circuitry is usually added that in some way connects the output back to one of the inputs. This circuitry is called the feedback loop. Feedback loops always act to equalize the difference between the two input voltages.
An op-amp circuit is easily analyzed by employing two 'golden' rules;