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Observatory

Unit 06 · Physics 3

Modern Physics

Where the classical picture runs out: relative time, quantised light, atoms with rungs, and decay no one can predict one nucleus at a time.

Work through them in order: each lesson assumes the one before it. Every lesson asks you to commit to a prediction, then lets you test it against a simulation of the real equations.

  1. 01

    Special Relativity

    One stubborn measured speed, and the price of keeping it: clocks that disagree, ships that shorten, and "at the same time" losing its meaning.

    Topics: Time dilation · Length contraction · Relativity of simultaneity · The Lorentz factor

    28 min4 checkpoints
  2. 02

    The Photoelectric Effect

    Turn the lamp up and nothing comes off faster. This is the experiment that made light countable, and the graph that hands you Planck's constant.

    Topics: Photons · Work function · Stopping potential · Planck's constant

    26 min4 checkpoints
  3. 03

    Atomic Spectra & Energy Levels

    Why a hot gas gives a handful of razor-thin lines instead of a rainbow, and why the ladder is drawn wrong in almost every textbook.

    Topics: Line spectra · Hydrogen energy levels · Emission and absorption · Ultraviolet and infrared series

    26 min4 checkpoints
  4. 04

    Quantum States & the Wavefunction

    A particle in a box has places it is never found, a lowest energy it cannot give up, and a probability that only moves when two levels share the state.

    Topics: The wavefunction · Probability density · Particle in a box · Stationary states

    26 min3 checkpoints
  5. 05

    Radioactive Decay

    A nucleus with no memory, no schedule and no way to be hurried, and a jar of them that keeps reliable time.

    Topics: Half-life · Decay constant and activity · Parent and daughter · Radiometric dating

    40 min4 checkpoints