Equipment:

• overhead projector - hallway
• Sargent-Welch circular ripple tank - in box near shelf 14
• wave source - shelf 8C
• Cenco 79550 power supply - hallway
• support rod and clamp
• two double banana leads
• extension cord
• beaker for filling the tank

Theory: A wave passing through a single slit of width d will diffract, the minima of the diffraction pattern coming at angles given by d sin(theta) = n lambda.

Description: The tank is set up over the projector on a movable cart. Only one source is used; the opening is produced by placing two pieces of plexiglas close together. They're movable, so the separation is set by hand. The frequency (and therefore wavelength) is controlled by the voltage. Tip 1 - the darker the room, the easier it is to see the pattern. Tip 2 - for best results, the overhead projector should be out of focus. It's best to have the lens closer to the tank then it would be when in focus.

Setup time: 20 minutes

References: (available in the demo room)

• Meiners, "Physics Demonstration Experiments", 18-6.