Experiment D3

Question 1

What is the aim of the experiment?

Answer 1

To determine the refractive index of glass by measuring the refracting angle and the angle of minimum
deviation for a prism.

Question 2

A relationship between nprism, Dmin and A can be derived as follows:

Answer 2

Question 3

In the determination of A the rays strike the prism as shown below, and you measure the angle between the
reflected rays.
▬▬► Prove that the angle between these reflected rays is 2A.

Answer 3

Question 4

If a prism is set at the position of minimum deviation for the green line in the spectrum, is it also at minimum deviation for the other colours? Explain your answer. (2)

Answer 4

Question 5

What is the purpose of the collimator on a spectrometer?

Answer 5

To provide a parallel incident ray for the grating/prism.

Question 6

What are the advantages of using the minimum angle of deviation to find the refractive index of a prism, rather than determining angles of incidence and refraction?

Answer 6

Measuring angles of incidence and refraction accurately is very difficult, whereas the angle of minimum deviation and refracting angle can be measured very accurately.

Question 7

Explain why rays travel symmetrically through the prism when the prism is set at the position of minimum deviation.

Answer 7

The angle of minimum deviation is the same if the direction of the incident ray is reversed so angles of incidence and refraction must be the same. Hence ray travels symmetrically through the prism i=i’.

Question 8

A prism is set up with a white light source. For certain positions of the telescope and the prism, the image is white, while for other positions the image is coloured. Explain.

Answer 8

If light is reflected from the prism faces it is white. If it passes through the prism faces, it produces a coloured image.