1. The problem statement, all variables and given/known data A beam of 3.55keV X-rays is directed at a crystal. As the angle of incidence is increased from zero, a first strong interferece maximum is found when the beam makes an angle of 18.0o with the planes of the crystal. Calculated d=5.67x10-10 from this (distance between adjacent planes) (c) Find the longest wavelength for which two interference maxima would be produced. 2. Relevant equations ## 2d\sin \theta = n\lambda ## 3. The attempt at a solution I set n=2, since we're looking for the second interference maxima, so then ## d\sin\theta = \lambda ## I was confused by where theta came from here, but to find the maximum wavelength I thought I would set ## \theta ## = 90, but this doesn't make physical sense to me.