Video: Evaluating the Output of AND Gates

The diagram shows an AND gate. If input A is 1 and input B is 1, what will the output be?

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Video Transcript

The diagram shows an AND gate. If input A is one and input B is one, what will the output be?

Okay, so, in this question, we can see that we’ve got an AND gate with two inputs and one output. Now we’ve been asked to work out what the output will be if input A is one and input B is one as well. To answer this question, let’s recall the truth table for an AND gate. So, here is the truth table for an AND gate.

We can see that the outputs are zero for whenever both of the inputs are not one. However, when both inputs are one, we can see that the output is one. And so, from this table we can see that when input A is one and input B is one, the output must be one. So, let’s label the output as one. And at this point, we’ve found the answer to our question.

However, it’s worth noting that we don’t need to memorise this entire truth table. And that there’s actually a simpler way of remembering what an AND gate does. The reason that this gate is called an AND gate is because the output can only be one if both input A and input B are one. And in every other scenario, the output will be zero.

We can see that from our truth table as well. When both inputs are zero, the output is zero. Even if one of the inputs is one, the output is still zero. The only way the output is one is if both input A and input B are one. Hence, our final answer is that if input A is one and input B is one, then the output is also one.

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