# Video: Evaluating the Output of an OR Gate Using a Truth Table

The truth table shows the output of an OR gate for various combinations of inputs. What is the value of 𝑝 in the table? What is the value of 𝑞 in the table?

01:23

### Video Transcript

The truth table shows the output of an OR gate for various combinations of inputs. What is the value of 𝑝 in the table?

Okay, so we’ve got a truth table that shows the behaviour of an OR gate. Now an OR gate behaves in the following way. First of all, it has two inputs, input 𝐴 and input 𝐵, and one output.

Now, if either of the inputs 𝐴 or 𝐵 are one, then the output is one. Otherwise, the output for an OR gate is zero. That’s why it’s known as an OR gate. Because if either input 𝐴 or input 𝐵 is one, then the output ends up being one as well.

Now, using that information, we need to work out the value of 𝑝 in the table. And 𝑝 is the value of the output for when the value of input 𝐴 is zero and the value of input 𝐵 is one.

Now, in this case, one of the inputs is one. We can see that input 𝐵 is set to one. And so the value of 𝑝 will be one as well.

Hence, that is our answer to this part of the question. The value of 𝑝 in the table is one.

Moving on then, let’s look at the next part of the question, which says “What is the value of 𝑞 in the table?”

Now, in the table, we can see that this is 𝑞. And this is the value of the output when input 𝐴 is set to one and input 𝐵 is set to one as well. Now, in this case, either input 𝐴 or input 𝐵 is one.

In fact, in this particular situation, both of them are one. And so the output which is the value of 𝑞 is also going to be one.

And, therefore, the value of 𝑞 in the table is one.