88 – Modern Physics
88.03 Glow discharge
88.06 Shadow from cathode rays
88.09 Photoelectric effect 
88.10 Planck’s constant demonstration
88.12 Electron diffraction
88.15 Spectra (also listed as 84.21, under Wave Optics)
88.16 Spectra, three gases
88.18 Electron cloud models
88.21 Fluorescence
88.22 Electroluminescence
88.24 Hologram
88.27 Crystal models
88.30 Radioactive sources detected by Geiger counter
A video of this demonstration is available (a link is on its page).