The formula for the refractive index of a prism is:
$$\mu = \frac{\sin \left(\frac{A + D_m}{2}\right)}{\sin (A/2)}$$
However, this requires me to find out the angle of minimum deviation ($D_m$). This would require me to take several readings, plot a graph, and then find the minimum point of the graph.
If I have two readings of the angle of emergence and angle of incidence, is there a way I can find the refractive index of the prism?
Best Answer
The following diagram should help:
We know of course the relationship between $\alpha$ and $\beta$ because the angle $A$ is known: $$\alpha + \beta = A$$
Next, we have the relationship between $i$ and $\alpha$ from Snell's law:
$$\frac{\sin{i}}{n}=\sin\alpha$$ and similarly for $\beta$:
$$\frac{\sin{e}}{n}=\sin\beta$$
This gives you three equations with three unknowns: $\alpha,~\beta,~n$.
I would recommend solving this numerically, or graphically. Simple example of a graphical solution:
I calculated the expected exit angle given an input angle of 45° and a refractive index of 1.543 - then calculated what exit angle I would get if I didn't know the refractive index. The error goes to zero when you have the right index...
Python code used to generate this: