Solution to task 521 from Chertov´s for extramural stud

Solution to task 521 from Chertov´s for extramural stud

521. A quartz plate with a thickness of d = 2 mm was placed between parallel nicols, as a result of which the plane of polarization of monochromatic light was rotated by an angle φ = 53 °. What is the smallest plate thickness dmin to make the field of view of the polarimeter completely dark?