# Question Video: Evaluating the Input of NOT Gates Physics

The diagram shows a NOT gate. If the output is 0, what must the input be?

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### Video Transcript

The diagram shows a NOT gate. If the output is zero, what must the input be?

Okay, so, in this question, we can see that we’ve been given a diagram of a NOT gate, otherwise known as an inverter. And the reason that a NOT gate that is known as an inverter is because it takes whatever is in the input and inverts it to give us the output. In other words, then, this is what the truth table of a NOT gate looks like.

When the input is zero, the output is one. And conversely, when the input is one, the output is zero. Or another way to think about it, is that whatever the input is the output is not. That’s why it’s known as a NOT gate.

So, we can see that we’ve got a NOT gate. And we’ve been told that the output is zero. So, we look at this row of the truth table. When the output is zero, the input is one. And so, we found the answer to our question. For a NOT gate, if the output is zero, then the input is one.

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