This is given under example of NOT GATE
why will the bulb short circuit if switch ON
@Siddhartha-Ghosh current follows the path with minimum resistance. When the switch is on the resistance of the path where the switch is connected becomes zero . Hence rather than the bulb , current flows through the switch that is the shorted path and the bulb doesn't glows hence called shorted that is simply it has no effect on the circuit any more.
@Siddhartha-Ghosh don't comfuse ON and OFF with OPEN and CLOSED