1. The problem statement, all variables and given/known data Calculate the wavelength of an electron which has 5eV of energy. 2. Relevant equations de Broglie's equation: lambda=h/p , kinetic energy equation: K=0.5mv^2 3. The attempt at a solution My attempt: I figured out that using de Broglie's wavelength equation was necessary for this question. but after changing around everything to get lambda = h/(2mK)^1/2, I kept on getting an incorrect answer. From comparing my methods to others I found that using Planck's constant's value in eV didn't work. What I really want to know is if I have to change the mass(m) to eV. The others had used Planck's constant's value in J/s and had multiplied the 2mK by the electron charge ( to change J/s to eV), and it had worked for them. Why is this?