Purpose:Demonstrate continuous spectrum using water as the dispersing medium.
Description: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 20 cm focal length cylindrical lens onto a slit. A 20 cm focal length convex lens then images the slit onto the screen through a prism consisting of an equilateral triangular plastic box filled with water. The spectrum created has less dispersion than that of a glass prism due to the smaller index of refraction of water. The spectrum of a quartz glass prism is shown at the right above for comparison.
Before showing the demonstration, invite students to predict how the different index of refraction will change the spectrum seen.