1. The problem statement, all variables and given/known data How wide is a single slit that gives its first minimum at 90°? 2. Relevant equations øp=p(λ/a) 3. The attempt at a solution Not quite sure what the answer is looking for but I'd guess I would need to solve for "a." So... 90°=(λ/a) Is there any more information I can gather from this problem? Any guidance would be a big help. Thanks guys!