1. The problem statement, all variables and given/known data A monochromatic light source is incident normally on a diffraction grating with 600 lines per mm. The beam passes through the grating and the fringes are observed on a screen 5m away. The apparatus is then immersed in a liquid whose refractive index is 1.3. In consequence the distance between the adjacent bright fringes is reduced by 0.45m. Find the wavelength of this light source in air. 2. Relevant equations 3. The attempt at a solution I derived the formula: x = n[tex]\lambda[/tex]D / d , where D = 5m and d = 1 / (600 x 10^3) = 1.67 x 10^-6m then I said: x - 0.45 = (1.3[tex]\lambda[/tex] x D x n)/ d but there are two unknowns, and this is where I'm stuck. I have the feeling that simultaneous equations will be needed. Thanks for any help!