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An OR gate is a digital logic gate with two or more inputs and one output that performs logical disjunction. The output of an OR gate is true when one or more of its inputs are true. If all of an OR gate's inputs are false, then the output of the OR gate is false. There are many ways to implement logic gates. Most frequently it is implemented by transistors. Here we are going to implement two input one output OR logic by using two transistors. This is based on the priciple of transistor switching action. If any of the switches S2 or S3 is closed, the transistor corresponding to that gets turned on and hence V5 becomes high and LED D1 starts glowing. The led can be turned off only by opening both switches.