The graph in the figure above is for a diffraction grating, showing sin as a function of wavelength for different orders of light. The red line corresponds to the second-order (m = 2) spectrum, and the blue line corresponds to the fourth-order (m = 4) spectrum.
(a) At what angle is the third-order bright spot for 400 nm
(b) For this grating, how many orders do we get for 600 nm
light? In other words, what is the largest possible value of m for
600 nm light?