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# Long description

Part (a) shows the symbol for an op-amp. This is a large triangle with two input wires entering one side. One input terminal is labelled with a + sign and the other with a − sign. An output wire exits the apex of the triangle opposite to the input side. Finally, two more wires enter the other two sides of the triangle, with a direction parallel to the input side. These are the wires that provide power from the power supply.

Labels have been added to the symbol to indicate the names that are generally used for the potentials. The input wires bring potentials V+ (for the + input) and V− (for the – input). The output wire provides a potential Vout. The power wires bring potentials VS+ and VS−.

Part (b) is a photograph of an op-amp in a package. It is a small black box with eight metallic legs (or pins), like a little bug with two extra legs. The rectangular top of the package has an indentation on one short side and a small circle in one corner near this indentation. Text on the package reads ‘M8420, LM, 741CN’.

Part (c) shows the diagram that we can use to understand the correspondence between the pins and the op-amp terminals. It is a rectangle with a triangular indentation marked on the top edge and a black dot in the top left-hand corner. This is used to orient the diagram with respect to the real package.

The four pins on the left are labelled, from top to bottom:

1 offset null

2 inverting input V−

3 non-inverting input V+

4 negative voltage VS−

The four pins on the right are labelled, from top to bottom:

8 pin not used

7 positive voltage VS+

6 output Vout

5 offset null

Inside the rectangle there is an op-amp symbol, and the wires are shown connecting the pins to the appropriate op-amp terminals. In this case, the – input is shown above the + input in the op-amp symbol.