Reference: L14
Category: Light and Waves
Purpose: Demonstrates refraction in a medium which is not isotropic.
Description: Various rhombs of Iceland spar (calcite). Place cardboard sheet with 2cm central hole on table of 3M projector, to limit aperture. Cover by metal plate with small “R” cut in it. Place a rhomb of Iceland spar immediately over this. Two images immediately appear, recalling the memorable “RR” (Rolls Royce) emblem. Show that, by rotating a Polaroid in the beam, one may extinguish either Mr. Rolls or Mr. Royce. (Try also holding Polaroid stationary and rotating the Iceland spar crystal; also remove Polaroid, and simply rotate the crystal – note that one “R” remains stationary, while the other “walks round it”. The former comes from the ordinary beam, which always passes normally through the crystal slab, since i = 0 and r = 0, while the latter comes from the extraordinary beam, which is deflected sideways in the crystal and does not obey the ordinary laws of refraction which apply to isotropic media.
