## Problem 1B.5: Units KeV

$c=\lambda v$

Julia Lindner 1I
Posts: 35
Joined: Fri Sep 28, 2018 12:17 am

### Problem 1B.5: Units KeV

This question is asking for you to calculate the wavelength of y-rays, and you are given the energy of the photons: 140.511 keV. Does anyone know what the unit keV means and how to use it in an equation? I tried using E=hv to find frequency and then using C= λv to find the wavelength. But I got stuck on units and how to cancel them.

Max Hayama 4K
Posts: 63
Joined: Fri Sep 28, 2018 12:16 am

### Re: Problem 1B.5: Units KeV

The unit eV stands for electron volt, and is approximately 1.602x10^19 J per 1 eV. Therefore, to begin this problem, you should convert 140.511 KeV to eV by multiplying by 1000, then multiply that by 1.602x10^19 to get the joules. Then use the energy equation to find frequency, and use this frequency in the speed of light equation to find wavelength.

Jonathan Omens 1K
Posts: 60
Joined: Fri Sep 28, 2018 12:15 am

### Re: Problem 1B.5: Units KeV

keV is a kilo-electron Volt, or 1000 electron volts. 1 Joule is equal to $6.24*10^{18}$ electron volts. So 1 Joule = $6.24*10^{15}$ keV.