Error Estimation for Refractive Index of Dielectric Material

[Mechdude]

Homework Statement

i did a lab on determination of refractive index of an opaque dielectric material, using the brewster angle. We took a couple of readings on a spectrometer at the position of complete extinction,
now how do i get the error estimate ? The angles were taken to the nearest minute

Homework Equations

$$tan \theta_B = \frac {n_t}{n_i}$$

The Attempt at a Solution

 

[lanedance]

you could look at dreivatives

you have the refractive index calculated in terms of the angle
$$n = f(\theta)$$

for a small change in angle
$$d \theta$$

what is the corresponding change in refractive index?
$$dn = \frac{df(\theta)}{d\theta}d\theta$$