Prismatic Spectrum Of White Light - Water Prism


Demonstrate continuous spectrum using water as the dispersing medium.


Bright point source with condenser lens and iris, 10cm focal length cylindrical convex lens, slit, 20cm spherical convex lens, and flint glass prism.

Setup Time

5 min




The bright point source is used to provide a continuous white light spectrum. Light from the point source is focused by a condenser lens with iris and a 10 cm focal length cylindrical lens onto a slit. A 20 cm focal length convex lens then images the slit onto the screen through a right-angle prism formed by the corner of a fish tank. Light internally reflected at the exit surface of the prism leaves the tank near the opposite corner and strikes the screen with opposite dispersion from the primary beam. The extra reflection causes the dispersion to reverse, just as the first and second order r