1. The problem statement, all variables and given/known data When a beam of monochromatic x-rays is incident on a particular NaCl crystal, Bragg reflection in the first order (ie w/ m=1) occurs at theta=20 degrees. The value of d = .28nm. What is the minimum voltage at which the x-ray tube can be operating? 2. Relevant equations 2dsin theta = m lambda (Bragg condition) lamba = hc/eV lambda (min) = 1240 nm / V 3. The attempt at a solution m = 1 so the Bragg condition gives lambda=.19 then I put that into V=hc/e lambda = 1240eV nm / e(.19nm) = 6526 V This gives me an answer with the right units, but I didn't take into account the difference between just lambda and lambda minimum. When I tried to put lambda into the equation for lambda min it just spit out the same thing I had (obviously).