The Wave Nature of the Electron Lecture Demonstrations
Energy is Proportional to Frequency
Commercial Photoelectric Effect Demonstrators are excellent for this purpose, but if one is not available:
Tape a piece of plastic diffraction grating to the lens of an overhead projector, as in Figure, and place an opaque cover on the Fresnel lens as shown, to project a continuous spectrum.
On the wall, tape a piece of phosphorescent sheeting  protected from room lights with a cover made from file folders (etc).
Dim the room lights, and project the spectrum on the phosphorescent material as shown. After several seconds, turn off the projector, and observe that the greatest phosphorescent intensity is below the visible range.
Electric Pickle Demonstrations
Use metal forks connected to the AC output of a Variac to excite the sodium wavelength in a dill pickle.