### Video Transcript

The red line shows an alternating current. Which of the following best explains why the black dashed line does not show this current rectified? (A) The black dashed line represents a different current frequency from the red solid line. (B) The black dashed line represents a different current amplitude from the red solid line.

Looking at our graph, we see that these two lines, the black dashed line and the red solid line, are in phase with one another. This means that at our beginning time, the phase difference between these two waves is zero and that zero phase difference continues through the propagation of these waves. This means that the frequency of these two waves is the same. Therefore, answer option (A), which says that these two lines represent different frequencies, cannot be correct.

Let’s consider then answer choice (B). And we recall that we’re looking for the best reason why the black dashed line does not represent the red solid line rectified. Current rectification is the process of taking alternating current, as represented by our red solid line, and modifying this current so that its direction is always the same. For a current that travels sometimes in one direction and sometimes in another, an alternating current, that is, rectification involves changing what we’ve called the negative values of this current so that while at any instant the current magnitude is the same as it was before, the current now only ever points in one given direction in a circuit.

This orange line we’ve drawn in is the rectified version of the red solid line. We see that this is different from the black dashed line in several ways. One of these ways, as indicated by answer choice (B), has to do with the amplitude of these two curves. The amplitude of a wave is its maximum displacement from equilibrium. The amplitude then of the black dashed line is given by this length, while the amplitude of the rectified current, or equivalently the amplitude of the red solid line, is given by this length. Because these amplitudes are different, the black dashed line can’t represent the rectified version of the red solid line. For our answer then, we’ll choose option (B).

This isn’t the only reason that the black dashed line does not represent the rectified version of the red solid line. But of our given answer options, it is the best explanation for why this is so. The black dashed line does not represent the rectified red solid line because the black dashed line represents a different current amplitude from the red solid line.