snell's law
posted by PEACE :) .
An equilateral prism of silica flint glassis used to refract white light. The indexof refraction of silica flint is 1.66 forviolet light and 1.62 for red light.
What is the angle of separation between
the violet and red ends of the rainbow
produced when the ray of white light is
incident at an angle of 50.0° with
respect to the normal?

From what i understand in this question, white light goes from air through the prism which splits it into red and violet. the question is asking about the angle between red and violet when it comes out in the air from the prism.
i used snells law to find the angle of refraction in the prism first.
going from air to prism
red => 1sin50 = 1.62 sin (theta)
theta (red) = 28.22
violet => 1 sin50 = 1.66 sin (theta)
theta (violet) = 27.48
i tried to use these angles to find the refraction angles from prism to air which gives me 50 again and sounds wrong.
not sure how to go about this problem.
please help.
thankyou 
There are are two refractions, you will have to draw a diagram and figure the effect of each refraction.
http://www.physicsclassroom.com/Class/refrn/u14l4a.cfm 
PRIMARY RAINBOW: Combine φ=4r−2i with Snell's Law to express the angle φ as a function of i and n only.
(a) Evaluate φ(i,n) for the following values (give your answers in degrees):
a.1) i=3∘, n=1.35
a.2) i=46∘, n=1.3