White light falls on a crown-glass prism with a refractive angle y = 60 °. Refractive indices for red and violet colors

White light falls on a crown-glass prism with a refractive angle y = 60 °. Refractive indices for red and violet colors are k = 1.524 and φ = 1.543. The violet ray passes with the smallest deflection; what is the angle b form between the rays of one and the other color upon exiting the prism? What will be the length of the spectrum of a star from red to violet on the plate if this prism is placed in front of a photographic camera with a focal length of 57 cm?

b = 1 ° 41 ‘. In the spectrum photograph, this will take about 17 mm.