1. The problem statement, all variables and given/known data An electron has a de Broglie wavelength of λ = 6.4e-10m. What is its speed? What voltage was needed to accelerate to this speed? 2. Relevant equations v=h/mλ KE = 1/2mv^2 3. The attempt at a solution I already determined that the speed is 1.136e6 m/s. Finding the voltage is what has me stumped. Using KE = 1/2mv^2, I found KE is 5.883e-19 J. I converted this to eV, so KE = 3.677 eV. With sig figs taken into account, the answer (I think) is supposed to be 3.7 eV but the online homework isn't accepting it. I feel like it shouldn't be hard, but I can't see what I did wrong. Any help would be appreciated!