 This one says an electron moves with velocity of 2.5 times 10 to the 8 centimeters per second. What is its wavelength? And then it gives the mass of an electron as being 9.11 times 10 to the negative 31 kilograms. So in order to figure out the wavelength from the mass and velocity, you have to use the Broglie's equation. So if you guys remember, I'd write that down. First thing is the wavelength equals Planck's constant divided by the mass times the velocity. And we have all of that stuff. Remember, Planck's constant, I have to give to you. It's not something that you're going to be memorizing. The one thing that you do have to know, though, is that joules is a derived unit. If you don't remember that, you're not going to be able to do this problem. So let me show you what I'm talking about. So remember, just like I just said, joules is a derived unit. So let's take it from joules to what it's derived from. So 6.66 times 10 to the negative 34. Now joules, what do we say, was kilograms meter squared per second squared, like that. But it's also multiplied by seconds. So we've got to multiply that by seconds on the numerator. So now, 1 divided by mass. So we've got the mass in kilograms already. So that's divided by 9.11 times 10 to the negative 31 kilograms. And then 1 divided by velocity. So that's just the inverse of what we have here. So on the top, we're going to put what? Very good, 1 second. 2.5 times 10 to the 8 centimeters on the bottom. So now let's try to cancel out stuff. So kilograms with kilograms, seconds with one of the seconds. The other seconds here, with the other seconds here. Now we've got meters squared divided by centimeters. So we're going to have to convert the centimeters to meters. So let's do that. You guys remember how many centimeters there are in a meter? 100 centimeters, 1 meter. So cancel, cancel. Cancel meters with one of the meters. And I want you to tell us the numbers. OK, it doesn't say what units to put it in. So wavelengths in meters, that's a good unit for a link. Does everybody agree with that? So this would be an O, all right, unit two. So again, figures, sorry, two significant figures. I'll get 2.9 to the negative 10. So that's a wave of an electron going back like this. So let's just convert this to nanometers, because 10 to the negative 10, that doesn't, you know, let's convert it to something that kind of is along the lines of what we know. Remember, visible light is from like 400 to 800 nanometers, right? So let's convert it to nanometers, OK? Because everybody's like 10 to the negative 10. Let's just convert it to nanometers just for fun. So how many nanometers are in a meter? You guys remember, 10 to the 9, 1 to the meter, to something that is something we're more familiar with. That's more kind of a reasonable number. Questions on this one? Pretty straightforward.