Modern Physics
Photoelectric effect, Bohr model, nuclear physics, radioactivity, and introductory quantum ideas.
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Photoelectric Effect
Khan Academy
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Einstein's Photoelectric Equation
Professor Dave Explains
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Bohr Model of the Atom
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Radioactive Decay
Michel van Biezen
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Half-Life
Khan Academy
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de Broglie Wavelength
Professor Dave Explains
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Notes
Photoelectric Effect
- Light ejects electrons only if f > f₀ (threshold frequency).
- Einstein: hf = φ + K_max; stopping potential eV₀ = K_max.
- Intensity affects number of electrons, not K_max (above threshold).
hf = φ + K_max
K_max = eV₀
E(eV) ≈ 1240/λ(nm)
Atomic Models & Quantum
- Bohr: angular momentum mvr = nℏ; energy levels E_n = −13.6 eV / n² (H).
- de Broglie: λ = h/p for matter waves.
- Photon momentum p = E/c = h/λ.
mvr = nℏ
E_n = −13.6/n² eV
λ = h/p
Nuclear Physics
- Radioactive decay: N = N₀ e^{−λt}; t½ = ln2/λ.
- Activity A = λN.
- Binding energy and mass defect: E = Δm c².
N = N₀ e^{−λt}
t½ = ln2/λ
E = Δmc²
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