A calcite rhomb rests on a printed dot and is viewed from directly above
PHYSICS · Subjective · Fermi University Physics · Optics & Photonics · Polarisation and anisotropic media · Polarisation and anisotropic media
Optics and Photonics, Ch Birefringence and crystal optics
Problem
A calcite rhomb rests on a printed dot and is viewed from directly above. Two images, P and Q, of the dot are seen. The observer records two tests. (a) Tilt test: when the rhomb is slowly rotated about the vertical (line-of-sight) axis, image P stays fixed at the centre while image Q traces a small circle around it. (b) Polaroid test: a polaroid sheet is rotated above the rhomb; image P disappears when the polaroid's transmission axis is set east-west; image Q disappears when it is set north-south. State which of P, Q is the ordinary image, and give the compass direction of the horizontal projection of the crystal's optic axis.