very narrow beam of white light is incident at 40.40° onto the top surface of a rectangular block of flint glass 11.8 cm thick. The indices of refraction of the glass for red and violet light are 1.637 and 1.671, respectively.

Calculate the dispersion angle (i.e., the difference between the directions of red and violet light within the glass block).
How wide is the beam when it reaches the bottom of the block, as measured along the bottom surface of the block?
When the rainbow-colored beam emerges from the bottom of the block, the exiting rays of light are once again parallel. Calculate the distance between the exiting red and violet rays (i.e., the thickness of the rainbow).