Logic OR gate
The logic Or gate is one of the simplest digital logic gates. The output of this gate is high, when one or all of its inputs are high. The OR gate is represented by the following Boolean function: X =A+B or X=B+A. (for a 2 input OR gate)
Two Input logic OR gate
The following picture shows the symbol of a 2 input OR gate, its truth table and how it can be made with switches.
By closing the A switch “or” the B switch the light will turn ON. “1″= closed, “0”= open, “1″= light on
Three Input logic OR gate
The following picture shows the symbol of a 3 input OR gate with its truth table and how it can be made with switches.
The lamp will turn ON when any of the switches (A or B or C) is closed. That is because, when any of the switches is closed, an electric current flow trough the lamp. The Boolean function is: X = A + B + C
Note: “1”, “high” and “ON” means the same.