Question on ray optics

[smn]

Hello there,

I've been working on the following question:

A thin prism with a refraction index of n=1.41 has a top angle of 5.7 degrees. Find the angle of deflection for a light ray that falls on the prism surface : (a) normally
(b) At an angle of 4 degrees

I have worked out the second part (b) using snell's law and some geometry techniques and get the answer of 2.3 degrees which i know is correct.

The first part of the question (a) i am struggling to workout although i do know the answer is suppose to be again, 2.3 degrees.

If anyone can shed any light (excuse the pun!) on the first part (a) of the question it would be greatly helpful.

Regards

Smn

 

[George Jones]

If the light ray falls normally on the surface (i.e., at right anglest to) there is no refraction - the light ray (ignoring partial reflection) just goes straight through. Consequently, only refraction at the second surface has to be considered. Use: geometry to relate the apex (top) angle to the angle of incidence at the second surface; Snell's law.

Regards,
George