Physics 5 — Modern Physics
Photons, the photoelectric effect, matter waves, special relativity’s γ, E = mc², and half-life dating.
Around 1900, physics hit two walls: light insisted on coming in chunks, and fast clocks insisted on running slow. The repairs — quantum mechanics and relativity — power your phone's chips and your GPS today.
- 01 Light comes in chunks: E = h·f A photon's energy is its frequency times Planck's constant — an absurdly small number, which is why light looks continuous. Green light, one photon at…
- 02 The photoelectric effect — Einstein’s Nobel Light ejects electrons from metal only if each photon individually carries enough energy to pay the exit fee (the work function W₀). Brighter-but-redder light…
- 03 Matter waves De Broglie's symmetric heresy: if waves are particles, particles are waves, with λ = h/(m·v). An electron's wavelength is atom-sized — that's why…
- 04 Special relativity — γ Nothing outruns light, and the universe enforces it with the Lorentz factor: γ = 1/√(1 − v²/c²). At everyday speeds γ ≈ 1 and nothing seems amiss; near c it…
- 05 E = mc² and half-life Mass is frozen energy at an outrageous exchange rate. One gram, fully converted: