Not gate

 

Study binary. Everything 0 and 1. 

Where there 0 you negate it with 1 and vice versa. That's not gate.

Refer truth table and diagram for circuit.

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Binary logic revolves around two values: 0 (false) and 1 (true). The NOT gate in logic circuits inverts the input. If the input is 0, the output is 1, and if the input is 1, the output is 0.

Truth Table for NOT Gate:

Input	Output
0	1
1	0

Circuit Diagram:

A NOT gate is represented as a triangle with a small circle at the output:

   ----|>o----
     Input    Output

In binary circuits, it's used for logical negation.

They are use useful in inverters.