1. The problem statement, all variables and given/known data I've got my exam in solid state physics tomorrow, and although I've understood most of the most complex subjects now, I feel I'm missing the understanding on one fundamental phenomena; Bragg reflection.. Throughout Kittel it's mentioned, that when we're at the first brillouin zone with k=½G, then we have standing waves. I don't think it's mentioned anywhere why though? Is there some equation from which I can easily realize, that when k=½G then the wavefunctions are made up of equal parts of waves traveling to the right and left?