Module 8: From the Universe to the Atom
11 dot points across 4 inquiry questions, in syllabus order. Each dot point has a focused answer, with exam-style questions and worked answers where available.
Inquiry Question 1: What evidence is there for the origins of the elements?
Big Bang and the origin of the elements. Hubble's law v = H_0 d as evidence for expansion, the cosmic microwave background as cooled relic radiation, primordial nucleosynthesis explaining the H/He ratio, and the timeline from the hot dense early universe to the present.
Stars and the elements. The Hertzsprung-Russell diagram, main sequence to red giant to white dwarf or supernova evolution, hydrogen to helium fusion via the p-p chain and CNO cycle, heavier-element fusion up to iron, and the supernova production of elements heavier than iron via the r-process.
Inquiry Question 2: How is it known that atoms are made up of protons, neutrons and electrons?
Millikan's oil drop experiment. Balancing gravity and electrical force on charged oil droplets between parallel plates, the equation mg = qE with E = V/d, the integer-multiple distribution of measured charges, and the value of the elementary charge e.
Structure of the atom. The Geiger-Marsden gold foil experiment, Rutherford's nuclear model replacing the plum pudding, and Chadwick's 1932 discovery of the neutron using beryllium-alpha collisions and conservation of momentum and energy.
Discovery and properties of the electron. Cathode ray tubes and the particle vs wave debate, Thomson's crossed-field experiment to measure the charge-to-mass ratio e/m, and his plum-pudding model of the atom.
Inquiry Question 3: How is it known that classical physics cannot explain the properties of the atom?
De Broglie matter waves. The hypothesis lambda = h/p applied to electrons and to macroscopic objects, the Davisson-Germer electron diffraction experiment, and the standing-wave reinterpretation of Bohr's quantised orbits.
Schrodinger's contribution to the atom. The wavefunction psi, the probability density |psi|^2, the time-independent Schrodinger equation for bound states, atomic orbitals (s, p, d, f) replacing Bohr orbits, and the resolution of multi-electron spectra.
Bohr model of hydrogen. Postulates of stationary orbits and quantised angular momentum, the energy levels E_n = -13.6 eV / n^2, the Balmer-Rydberg formula 1/lambda = R (1/n_f^2 - 1/n_i^2), spectral series (Lyman, Balmer, Paschen), and the limitations of the model.
Inquiry Question 4: How is it known that human understanding of matter is still being refined?
Standard Model. Three generations of quarks and leptons, the four fundamental forces and their gauge bosons (photon, W and Z, gluons, graviton), the role of particle accelerators in producing and detecting these particles, and the place of the Higgs boson.
Radioactive decay. Alpha, beta-minus, beta-plus and gamma decay with nuclear equations, the decay law N = N_0 e^(-lambda t) and N = N_0 (1/2)^(t / T_1/2), and the relation lambda T_1/2 = ln 2.
Nuclear energy. Mass defect Delta m = Z m_p + N m_n - m_nucleus, binding energy Delta m c^2, the binding-energy-per-nucleon curve with its iron peak, energy release in fission (heavy nuclei split) and fusion (light nuclei combine), and worked examples for both.