NOT Gate:

A logic gate that inverts a digital input signal is known as a NOT gate. Consequently, the NOT gate is also referred to as an inverter (not to be confused with a power converter). When the input to the NOT gate is low, the output is always high (logic 1). (Logical 0).

When the input is high, the output of the NOT gate is always low (logic 0). else it is (Logic 1). This is the logic symbol for a NOT gate:

Formula:

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