## Diffraction

• WM2.1 Bragg Diffraction Using Microwaves

This is done in the lab. A styrofoam cube has 100 steel balls symmetrically placed to be like atoms of a cubic crystal. Using a microwave source and detector at different angles, Bragg diffraction can be seen on an oscilloscope attached to the detector. The answers can be compared to the theoretical value 2dsinA =nl, where A is the usual angle and l the wavelength.

• WM2.2 Laser and Screen

The screen that runs diagonally from the back wall to the first pillar on the north side of the lecture hall should be used. The laser is placed on a rolling table on the south side of the lecture hall, leveled by lab jacks and the slit plate is placed on a optical bench. The room lights must be turned off to see the diffraction pattern on the screen. The pattern seen on the screen is the intensity of the constructive and destructive waves. The best pattern consists of approximately five intensity peaks.

• WM2.3 Overhead Representation of Young's Experiment

This is two sheets of transparent plastic with sets of concentric circles. Placing these on the vu graph and moving them back and forth will show a Moire pattern with peaks and valleys where the waves interfere.

• WM2.4 Young's Experiment using Microwaves

The apparatus consists of two microwave generators and one meter. The generators are placed a small distance away from each other, facing the same direction. The meter is carried by the instructor in front of the generators. The meter, big enough so that the class sees the needle move, shows peaks and zeros of the interfering waves. An AC hum can be used as an auditory indicator of intensity. The wavelength of the microwaves is 12cm.

• WM2.5 Young's Experiment using Sound

The idea is the same as above. The difference is that an oscillator puts out a sound through two speakers and a microphone attached to an oscilloscope is used to detect the intensity.