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How does OR gate work?
An 'OR' gate is like two or more switches positioned in parallel. Only one switch desires to be closed (' a value of '1') in order to make the light (output) turn 'ON' with a value of '1'.
For the above two-input OR gate, output Z is high when either input A or input B is high, or when both A and B are high; Z is low only when both of them are low. ( Thomas, L Floyd 2006, digital fundamental 9th edition)