Dawn of Modern Physics — three ways to learn it.

The complete written lesson — the basics of special relativity, Planck's quantum and E = hf, the photoelectric effect with work function and stopping potential, the Compton effect, wave–particle duality and the de Broglie wavelength, and the uncertainty principle.

As you scroll, a live animated panel brings every idea to life: photons strike a metal plate and knock electrons free, the stopping voltage rises with frequency, a photon recoils off an electron, and a moving particle spreads into a de Broglie wave.

Run the photoelectric experiment on a safe, virtual bench — vary the light frequency, read the stopping voltage at each frequency, and plot the graph whose slope gives Planck's constant h.