# Minimum deviation in a Prism - Help Please!

## Homework Statement

A ray of light is incident in air at an angle of 40 degrees to the normal to one face of a 60 degree glass prism. Calculate the angle through which the ray has been deviated by the time it emerges from the prism. (refractive index of glass wrt air is given as 1.50)

## Homework Equations

I tried using the formula:
n1 = sin(A+D)/2 $$\div$$ sin(A/2)

where D = 2i - 2r & A = 2r

## The Attempt at a Solution

i am not sure how to approach the question, i dont know where to include the angle of incidence, the solution is supposed to be 38.5 degrees. Please, can someone help me out! thanks!

## The Attempt at a Solution

ehild
Homework Helper
Physics is not just plugging in data into a formula you do not understand.

Sketch the problem. Draw an equilateral triangle: this is the prism.
Draw the incident light ray to one side of the prism, making 40° angle with the normal. Apply Snell's law. Draw the refracted light inside the prism. Calculate the new angle of incidence at the side it arrives at. Apply Snell's law again, to get the angle of the emerging light in air. Find the angle between the original light ray and the emerging one.

ehild