You are given prisms made of crown glass and flint glass with a wide variety of angles. Suggest a combination of prisms which will (a) deviate a pencil of white light without much dispersion, (b) disperse (and displace) a pencil of white light without much deviation.
Answers
Given prisms made of crown glass and flint glass with a wide variety of angles.
a)
- Place the two prisms beside each other as shown in the attachment
- Ensure that their bases are on the opposite sides of the incident white light, with their faces touching each other.
- When the white light is incident on the first prism, it gets dispersed.
- when this dispersed light is incident on the second prism, it will recombine and white light will emerge from the combination of the two prisms.
(b)
- When we arrange the two prism as suggested above .
- Adjust (increase) the angle of the flint-glass-prism so that the deviations due to the combination of the prisms become equal.
- This combination will disperse the pencil of white light without much deviation.
Answer:
Explanation:
A
The two prisms should be arranged such that the dispersion produced by one prism is cancelled by the second prism. This way is called as the direct vision prism. The dispersion of the crown glass prism is less than the flint glass prism.
So, the flint glass prism of smaller angle will be suitable with a crown glass prism of larger angle.
B
To disperse without any deviation, the flint glass prism of greater angle close to each other in opposite directions is required so that the deviation is equal and opposite. So, in final combination the flint glass prism will have smaller angle than crown glass prism because of their refractive indies.