In a logic circuit, the OR gate outputs a 1 when?

In a logic circuit, the OR gate outputs a 1 when?

• A. Only when all inputs are 1
• B. At least one input is 1
• C. When no inputs are 1
• D. Only when exactly two inputs are 1

Answer: (B)

An OR gate performs a disjunction: its output goes high as soon as any input is high. For two inputs, the output is 0 only when both inputs are 0; if either input is 1, or both are 1, the output is 1. With more inputs, the output remains 1 as long as at least one input is 1. So the correct description is that the OR gate outputs a 1 when at least one input is 1. The other statements don't fit: requiring all inputs to be 1 describes an AND-like condition, requiring no inputs to be 1 would give 0, and requiring exactly two inputs to be 1 is too restrictive because the output would also be 1 when there is exactly one input 1 or more than two inputs 1.

An OR gate performs a disjunction: its output goes high as soon as any input is high. For two inputs, the output is 0 only when both inputs are 0; if either input is 1, or both are 1, the output is 1. With more inputs, the output remains 1 as long as at least one input is 1. So the correct description is that the OR gate outputs a 1 when at least one input is 1. The other statements don't fit: requiring all inputs to be 1 describes an AND-like condition, requiring no inputs to be 1 would give 0, and requiring exactly two inputs to be 1 is too restrictive because the output would also be 1 when there is exactly one input 1 or more than two inputs 1.