MDCAT Modern Physics 2026 — Photoelectric, Atomic, Nuclear

Photoelectric Effect

• Einstein equation — hf = φ + KE_max
• Threshold frequency — f₀ = φ/h
• Stopping potential — eV_s = KE_max

Bohr Model

• Energy level — E_n = −13.6/n² eV (hydrogen)
• Radius — r_n = 0.529 × n² Å
• Transition — E_photon = E_final − E_initial

Nuclear Decay

• Activity — A = λN; N = N₀e^−λt
• Half-life — t_1/2 = ln(2)/λ = 0.693/λ
• Alpha decay — mass −4, atomic −2
• Beta decay — mass unchanged, atomic +1

Pair with our Physics formula sheet.