PURPOSE: To show total internal reflection and the critical angle.
DESCRIPTION: Use the black board optics semi circular disk, as shown. A
single slit ray projector is used to produce a narrow ray of light. Rotate the
semicircular slab of plexiglass with the light ray entering and exiting through the curved
surface. Start with the ray incident nearly perpendicular to the flat internal surface, as
shown at the left. Slowly and carefully rotate the semicircular slab until the
critical point is reached and total internal reflection is obtained, as shown at right.
The Brewster angle can also be demonstrated by rotating the semicircular slab so that the
transmitted refracted ray and the internally reflected ray are perpendicular. See 6h20.10.
EQUIPMENT: Black board optics as photographed, portable white board.
Updated by Jun Qi in 3/22/2000