Topic 8 of 8 · Form 6
Quantum, nuclear, medical physics and astronomy
Photon energy E = hf; the photoelectric effect hf = Φ + ½mv²max; threshold frequency; wave–particle duality and electron diffraction (λ = h/p); energy levels and line spectra.
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Quantum physics
Photon energy E = hf; the photoelectric effect hf = Φ + ½mv²max; threshold frequency; wave–particle duality and electron diffraction (λ = h/p); energy levels and line spectra.
Worked example: Light of wavelength 400 nm falls on a metal of work function 2.3 eV. Find the maximum kinetic energy of photoelectrons in eV.
E = hc/λ = 4.97 × 10⁻¹⁹ J = 3.11 eV → KEmax = 0.81 eV
Nuclear physics
Mass defect and binding energy (E = Δmc²); binding energy per nucleon curve; fission and fusion; radioactive decay A = λN, N = N₀e^(−λt), t½ = ln 2/λ.
Medical physics
Ultrasound (acoustic impedance Z = ρc, reflection coefficient), X-ray imaging and attenuation I = I₀e^(−μx), CT scanning, PET scanning.
Astronomy and cosmology
Luminosity, radiant flux intensity F = L/(4πd²), standard candles, Wien's law λmax T = constant, Stefan–Boltzmann law L = 4πσr²T⁴, redshift and Hubble's law v = H₀d, the expanding universe.
Check yourself
- A source has a half-life of 8 days. Find its decay constant.
- What does a line emission spectrum show?
- State Hubble's law.
Show answers
- λ = 0.693/(8 × 86 400) = 1.0 × 10⁻⁶ s⁻¹
- Electrons move between discrete energy levels, emitting photons of specific frequencies.
- The recession speed of a galaxy is proportional to its distance (v = H₀d).
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