Question Video: Inspecting the Waveforms of Laser-Produced Waves Physics

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?

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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.

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