Question

Natural monochromatic light falls on a system of two crossed Nicol prisms between which a quartz plate cut at right angles to its optical axis is inserted. Find Pal the minimum thickness of the plate at which this system will transmit η = 0.30 of luminous flux if the specific rotation constant of quartz is equal to α = 17 ang.deg/mm.

Answer 1

If l₀ intensity of natural light then 

 = intensity of light emerging from the polarizer nicol. 

Suppose the quartz plate rotates this light by φ, then the analyser will transmit

For minimum d we must take the principal value of inverse sine. Thus using α = 17 ang deg/mm.

d_min = 2.99 mm.