Video Transcript
The diagram represents the
resultant waveform of the waves emitted from a laser light source. Which of the following diagrams
most correctly represents a group of the waves emitted from the laser light
source?
All right, so when our question
talks about the diagram, it’s referring to this waveform right here that we see in
purple. It tells us that this is the
resulting waveform from the combination of a series of waves emitted from a laser
source. We’re then told about these other
diagrams labeled I and II, which shows two different groups of waves. One of these two groups, we’re
told, correctly represents the waves emitted from the laser source.
So, we could put the question this
way. When we combine the waves shown in
group I and when we combine the waves shown in group II, which combination will
yield the resulting wave in purple that we’re shown here? We can figure out the answer to
this question by looking closely at this waveform. Notice that it has a very
consistent and regular wavelength all throughout the length of the waveform. Along with that, the displacement
of the wave from equilibrium goes through very even cycles. The wave always reaches the same
maximum value here and here and here and so on, as well as the same minimum values
here and here and here and so on and so forth.
If we were to add up a series of
waves in order to create this resultant, then those individual waves would need to
be very like one another. They would need to have the same
wavelength, for example. That’s what leads to this resulting
wave having the same wavelength all throughout. And they would also need to line up
with one another so all the peaks were in line and all the troughs were in line. In other words, the waves must have
a phase difference of zero or be in phase with one another.
Knowing this, as we compare the
waves in diagram I with those in diagram II, we can see that the waves in diagram I
meet our conditions. They’re in phase, and they have the
same wavelength as one another all throughout, while the waves in diagram II have
varying phase relationships from left to right and also different wavelengths from
one another. It’s hard to predict exactly what
the result of adding all these waves together would be. But we can be confident that it
wouldn’t be as regular and orderly as this resulting waveform. Such a well-ordered result requires
very similar waves being added together.
And so, we see that the waves in
diagram I most correctly represent a group of waves emitted from this laser light
source.
