This document covers concepts related to waves and electromagnetic radiation. It defines key terms like wavelength, frequency, and discusses the inverse relationship between them. It also outlines the electromagnetic spectrum in order of wavelength from gamma rays to radio waves. Specific wavelengths are given for colors of visible light. The document also discusses photon energy and Planck's constant, the photoelectric effect, and quantum mechanical concepts like quantized energy levels and the wave-particle duality of electrons and photons.