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Atomic & Nuclear Physics
This chapter covers light as photons, energy levels in atoms, and the changes that happen inside the nucleus. You will apply the photoelectric equation, Bohr energy levels, decay equations, half-life, and mass-energy equivalence to fission and fusion.
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What this chapter covers
- Photons & the Photoelectric Effect. The photoelectric effect is the MCAT's favorite proof that light comes in packets. Know what depends on frequency and what depends on intensity.
- Bohr Model, Spectra & X-rays. Energy-level diagrams turn spectral lines into subtraction: emitted photon energy is the gap between two levels.
- Radioactive Decay Types. You will balance nuclear equations for alpha, beta, and gamma decay. The bookkeeping is conservation of mass number and charge.
- Half-Life & Decay Kinetics. Half-life questions are pure halving arithmetic. Count the half-lives first and the answer follows.
- Mass Defect, Binding Energy, Fission & Fusion. E = mc² explains why nuclei weigh less than their parts and why both splitting heavy nuclei and joining light ones release energy.
Key points to know
- E = hf; each photon frees at most one electron
- K_max = hf − φ; threshold f₀ = φ/h
- E_n = −13.6/n² eV; ionization energy from n = 1 is 13.6 eV
- Emitted photon energy = difference between two levels
- α: loses ⁴₂He (Z − 2, A − 4)
- β⁻: n → p + e⁻ + ν̄ (Z + 1, A same); β⁺ and electron capture: Z − 1
- Fraction left after n half-lives = (½)ⁿ, with n = t/T½
- λ = 0.693/T½; activity A = λN in becquerel (decays/s)
Try a practice question
In the photoelectric effect, what determines the maximum kinetic energy of the ejected electrons?
- Light intensity and exposure time
- Photon frequency and the metal's work function
- Only the number of photons
- Only the temperature of the metal
Show the answer
B. K_max = hf − φ. It depends on the photon frequency and on the metal's work function. Intensity changes how many electrons are emitted, not how energetic each one is.
Common questions
What does this chapter cover?
Atomic & Nuclear Physics covers Photons & the Photoelectric Effect, Bohr Model, Spectra & X-rays, Radioactive Decay Types, Half-Life & Decay Kinetics, Mass Defect, Binding Energy, Fission & Fusion.
What should I know first?
E = hf; each photon frees at most one electron K_max = hf − φ; threshold f₀ = φ/h E_n = −13.6/n² eV; ionization energy from n = 1 is 13.6 eV
25 original practice questions accompany this chapter in the app. Spaced review brings missed ideas back at the right time; it helps memory but cannot promise you will not miss an idea again.