 So this question says, a hospital x-ray gun that has a wavelength of 15.0 nanometers emits x-rays. What is the energy of one of these x-ray photomic particles? So anyways, what we have to remember is two equations. So E equals N, H, nu, C equals lambda, and nu being the frequency and lambda being the wavelength. So if we rearrange this equation, we get nu equals C over lambda. So we're going to plug that into this equation. So N, H, C divided by lambda. OK, H and C are constants given to you. So C, 2.998 times 10 to the 8 meters per second. And H is Planes constant, so this is to be like 6.626 times 10 to the negative 34 joules seconds. So N in this case, since it just wanted one photon, was 1. That should give us everything we need, because we've got wavelength here. The only thing that is the problem is that we've got this C in meters and wavelength in nanometers, so we're going to have to convert nanometers to meters. So how do we do that? If you don't remember, this is one that you want to remember. So there's 1 times 10 to the 9 nanometers per 1 meter. So let's go ahead and plug all of that into the calculator and see what we get. OK, so well, we don't have to convert it. Joules is the energy unit in 1. So H is 6.6234, and that's C, 2.998 times 10 to the 8 to the power 1 second. And then 1 over lambda 1, it's upset. OK, so if we look here, we've canceled seconds there, meters there, and we get joules for our units. That's good energy units. It didn't say to give it in kilojoules or millijoules or anything like that, so let's just stick with joules. So this is just one photon, so we would expect it to be a very small number. And the number I got to 3 sigma bigs is 1.32 times 10 to the negative 17 joules per x-ray photon. OK? I just wanted to know, how do you know it's a 1 photon? But can you just assume that, because it's an accident? Yeah, so when it doesn't ask you, it's expecting you to do one photon. It'll tell you sometimes it'll say, what's the energy of one mole of photons? And in that case, you do 6.022 times 10 to the 23rd. You just got to remember this. That's where I didn't know where to plug in, because I didn't know what to do with n. That n there, you just got to watch it, OK? So that's the number of, in this case, photons. That's what I meant. That's a specified one. Yeah, just choose one, yeah? Any questions on that one? OK.