W7-03 Particles with zero rest mass

This lecture from the Physics Lectures channel discusses particles with zero rest mass, focusing on photons. The instructor begins by reviewing the relativistic energy and momentum equations, noting that as velocity approaches the speed of light, energy and momentum tend to infinity for massive particles. However, by setting the rest mass to zero, these equations become finite and yield the relation E = pc for massless particles. The lecture then explores the historical development of the concept of light as particles, from Newton’s corpuscular theory to the wave theory and the photoelectric effect, which necessitated the particle model. It also touches on the blackbody radiation spectrum and the hydrogen spectrum, both of which require quantization of light. The instructor emphasizes that electromagnetic radiation exhibits both wave and particle properties, and for massless particles, the energy and momentum are related to frequency and wavelength via Planck’s constant. The lecture concludes by deriving the key equations for massless particles, E = hν and p = h/λ, and highlights their importance in quantum physics.