PURPOSE: To identify the source of penumbra regions.

DESCRIPTION: Combined red and green filters project nearly white light on a screen. When the foam sphere is inserted between the sources and the screen, the penumbral regions take on the color of the filter through which the light in that region has traveled, because the other color has been blocked by the disc. The umbra, where light from both sources is blocked, is nearly black.

SUGGESTIONS:

REFERENCES: (PIRA 8A10.30)

EQUIPMENT: Double point source with red and green color filters, foam ball on 18" wooden dowel.

SETUP TIME: None.