Keep the modern-physics branch bounded with the photoelectric effect, atomic spectra, de Broglie matter waves, the Bohr model, and radioactivity / half-life so threshold emission, discrete lines, matter wavelength, quantized hydrogen levels, and probabilistic nuclear decay all stay tied to compact, visually honest benches instead of detached historical anecdotes.
This topic stays intentionally compact for now. One module keeps the modern-physics turn anchored on a controllable lamp, metal surface, and collector so you can separate frequency from intensity, threshold from brightness, and stopping potential from emission rate. The next keeps an energy ladder and observed spectrum on one shared bench so discrete lines point toward quantized structure. de Broglie matter waves then add a compact momentum-to-wavelength bridge with one local spacing sketch and one fixed loop fit. The Bohr-model page specializes that evidence into hydrogen series, allowed transitions, and bounded historical orbit language while staying explicit that it is not the final quantum description. Radioactivity and Half-Life then keeps one bounded sample tray and linked decay curves in view so single-nucleus chance and large-sample regularity can be read honestly without turning the topic into a full nuclear-physics subsystem.
Best first concepts
The topic page keeps these starts in their own compact row so the first screen is about orientation and next action, not stacked feature cards.
Use one compact lamp-to-metal bench to see why light frequency sets electron emission, why intensity alone fails below threshold, and how stopping potential reads the electron energy honestly.
Light and matter
Strong first stop for getting into this topic without scanning the whole library.
Link discrete emission and absorption lines to allowed energy-level gaps with one compact ladder-and-spectrum bench that keeps transitions, wavelengths, and mode changes tied together.
Quantized line spectra
Strong first stop for getting into this topic without scanning the whole library.
Use one compact matter-wave bench to see how particle momentum sets wavelength, why heavier or faster particles get shorter wavelengths, and how whole-number loop fits form a bounded bridge toward early quantum behavior.
Matter waves and quantum bridge
Strong first stop for getting into this topic without scanning the whole library.
Use a compact hydrogen bench to connect quantized energy levels, allowed transitions, and named spectral-line series while staying clear that Bohr is a useful historical model rather than the final quantum description.
Hydrogen energy levels
Strong first stop for getting into this topic without scanning the whole library.
Use one compact decay bench to see why each nucleus decays unpredictably, why large samples still follow a regular half-life curve, and how to read remaining-count graphs honestly.
Nuclear decay and chance
Strong first stop for getting into this topic without scanning the whole library.
Grouped concept overview
Each group is authored for this topic, but the actual concepts, progress badges, and track cues still come from the canonical concept metadata and shared progress model.
Group 01
Use one compact emission bench, one compact ladder-and-spectrum bench, one momentum-to-wavelength bridge, and one bounded hydrogen Bohr bench to connect threshold frequency, discrete spectral lines, matter-wave fits, and named series without widening into a full quantum platform.
Use one compact lamp-to-metal bench to see why light frequency sets electron emission, why intensity alone fails below threshold, and how stopping potential reads the electron energy honestly.
Strong first stop for getting into this topic without scanning the whole library.
Link discrete emission and absorption lines to allowed energy-level gaps with one compact ladder-and-spectrum bench that keeps transitions, wavelengths, and mode changes tied together.
Strong first stop for getting into this topic without scanning the whole library.
Use one compact matter-wave bench to see how particle momentum sets wavelength, why heavier or faster particles get shorter wavelengths, and how whole-number loop fits form a bounded bridge toward early quantum behavior.
Strong first stop for getting into this topic without scanning the whole library.
Use a compact hydrogen bench to connect quantized energy levels, allowed transitions, and named spectral-line series while staying clear that Bohr is a useful historical model rather than the final quantum description.
Strong first stop for getting into this topic without scanning the whole library.
Group 02
Branch into one compact radioactivity bench where individual decays remain probabilistic, but large samples still produce a regular half-life pattern that can be compared honestly with the rest of the modern-physics evidence.
