Basic Operations of Digital Electronics (Physics-19.11): There are many things which have only two possible states. For example a circuit can be either on or off. It cannot have a third state. Similarly, a given statement would be either true or it would be false. The given answer of a question would be either right or it would be wrong. A switch would be either open or closed. Such things which can have only two possible states are known as Boolean variables.

The two states of Boolean variables are usually represented by the digits 0 and 1. For example, a closed switch is represented b 1 and an open one by 0. If there are two switches and we say that they are in state 1, then it would mean that both of them are closed. Suppose we form a circuit by connecting some resistors, two switches and a battery. As a result of this connection, some current may pass through the circuit.


So we call the current in this case as output. This output also has two states. Depending upon the states of the switches, the current either would pass or it would not pass. Thus the output current is also a Boolean variable. In case the current is passing, we can say the value of output is 1 and it is 0 when no current is passing. Whether the value of the output would be 1 or 0, it depends upon the values of Boolean variables which specify the state of the switches. In this example, the switches form the input Boolean variable because the value of output depends upon the state of these variables. Now the question arises that if the values of input variables of a circuit or a system are known, then that can we determine the value of the output? In order to solve this problem, digital electronics requires three basic operations known as AND operations, OR operation and NOT operation. Let us see what are these basic operations?