# Question Video: Finding the Peak Value of an Alternating Current Physics • 9th Grade

The graph shows the current in a wire over time. What is the peak value of the current?

01:27

### Video Transcript

The graph shows the current in a wire over time. What is the peak value of the current?

Okay, so looking at this graph, we indeed see the current in amperes plotted against the time in seconds. And we’re told that this is the current running through some wire. Looking at this plot, we can see that clearly the current doesn’t stay the same, but it varies in time. It starts out at this maximum value here, and then it decreases down to zero. Then it goes into negative values. That means the current changes direction in its circuit, then comes back up to zero and then returns to this original maximum value. And as time goes on, this cycle continues.

Our question asks about the peak value of the current. This is the highest value it will ever achieve at any time we can see. Now, because the current in this plot is regularly switching direction, that’s what we saw when it moves from positive values to negative values and then back. That means the current in this wire is alternating current. This tells us that when our current reaches its peak value, it doesn’t do that just once. But, rather, it does it in a cycle.

And looking at our graph, we can see where our current touches over and over again on this maximum or peak value. It achieves that peak value here and here and here as well as here. And as we look on the vertical access to see what that peak value is, we see that it’s 0.4 amperes. This is the maximum positive value our current achieves. And, therefore, it’s the peak value of the current.