# Homework Help: An A.H. Pfund's method

1. Feb 18, 2013

### deltafee

1. The problem statement, all variables and given/known data
An A.H. Pfinds's method for measuring the index of refraction of glass is illustrated in the figure. One face of a slab of thickness t is painted white, and a small hole scraped cleat at point P serves as a source of diverging rays when the slab is illuminated from below. Ray PBB' strikes the clear surface at the critical angle and is totally elected, as are rays such as PCC'. Rays such as PAA' emerge from the clear surface. On the painted surface, there appears a dark circle of diameter d surrounded by an illuminated region, or halo.

diagram: https://dl.dropbox.com/u/77575413/68.png [Broken]

Part A:
The equation for n in terms of the measured quantities d and t. is n=(1+(16t^2)/d^2)^(1/2)

Part B:
The diameter of the dark circle if n=1.52 for a slab of 0.06 cm thick is 2.09×10(-2)m

Part C:
If white light is used, dispersion causes the critical angle to depend on color. Is the inner edge of the white halo tinged with red light or with violet light explain.

2. Relevant equations

n=(1+(16t^2)/d^2)^(1/2)

3. The attempt at a solution

I was able to do part A and B but I am not sure about Part C.

I said the white halo is tinged with violet light since violet light has a higher index of refraction. Is this true or did I mess up.

Last edited by a moderator: May 6, 2017
2. Feb 19, 2013

### Basic_Physics

What color is dispersed most when white light goes through a prism?
What does this tell you about the refractive index/colour of light relationship?
How is the refractive index related to the critical angle?