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welcome to our fourth example video. Looking at the fundamentals of modern physics in this video, we're going to look at the wavelength of like 500 nanometers and find the energy associated it with it. We know from Einstein that ye is equal to H times F, which means that given the relationship between C lambda and if we can then rewrite energy in terms of the wavelength as Plank's constant multiplied by the speed of light divided by the wavelength of the light. Typing this in gives us the answer. Three 0.978 times, 10 to the negative 19 where we used three times, 10 to the eight for C. And then, if we wanted to convert this, then into electron volts, we could multiply this by one Evian every 1.6 times, 10 to the negative. 19. Jules and we would come up with an E V of 2.49 e. V. You can see that's a much more reasonable number to write down Just why we prefer to use E V in situations like this. On the other hand, consider a copper electrode, which has a work function, eh? Not equal to 4.65 What is the color of light? The minimum color of light. That is the wavelength of light that will start to produce. Uh, that will start to produce electrons out of a copper electrode. Well, it needs to be greater than this. We need energy that's greater than this. So let's go ahead and plug it in, and we'll know that that will be the minimum wavelength that we need. Okay, So solving for Lambda here, Lambda is equal to H C over E, and we can go ahead and type in what we had before. Except again, we will need to convert from E V into jewels. Now, there are some people who like to express Plank's constant in terms of jewels or in terms of E V. Um, and that may be written down inside your book somewhere you can use either one. Each one works, Justus. Well, what this gives us is a wavelength of 267 nanometers, so you can see this is a lower wavelength. The lower wavelength corresponds to a higher energy, and in fact, this wavelength here is again almost within the visible, um 267 nanometers is just below what we would consider for being visible with I believe it is read. Yes, Read is approximately. I'm sorry. Violet is approximately 450 to 400 nanometers, which means that we have just below there. So we're just too energetic, which means that this would be considered the ultraviolet range. Now, some people confuse this, and they think that low energy means low wavelength. But in fact, high energy means low or rather short wavelength.

University of North Carolina at Chapel Hill