1. The problem statement, all variables and given/known data using the formula Δy = λL/ d calculate the fringe separation (d) for the red and blue light used in the experiment 2. Relevant equations as above 3. The attempt at a solution So I rearranged the equation to read d = λL / Δy and I'm fine with the math, but I don't understand what wavelength to use, as the following question is. Using (d) found in the previous question, find the wavelength of the red and blue light used in the experiment. So say I have Δy = 5.00 x 10-4m L = 0.25 m The equations would be d = 0.25λ / 5.00 x 10-4 am I supposed to use a separate equation for this formula or do I just use an approximate length of red light such as 450nm?