§-Module

Module 7: The Nature of Light

8 dot points across 3 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 is light?

Describe the electromagnetic spectrum in terms of frequency, wavelength and photon energy, and outline how Maxwell's equations conceptually predict electromagnetic waves travelling at the speed of light

Electromagnetic spectrum. Frequency, wavelength and photon energy across radio to gamma rays, the relations c = f lambda and E = hf, and how Maxwell's equations conceptually predict EM waves at the speed of light.

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Analyse the wave model of light using Young's double-slit experiment, single-slit diffraction and polarisation, and apply Malus's law I = I_0 cos^2 theta to polarised light

Wave model of light. Young's double-slit interference with d sin theta = m lambda, single-slit diffraction, polarisation as evidence light is transverse, and quantitative use of Malus's law.

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Inquiry Question 2: What is observed when light interacts with matter?

Investigate emission and absorption spectra, distinguish continuous, line emission and line absorption spectra, and analyse stellar spectra to identify chemical composition, surface temperature and motion

Spectroscopy. Continuous, emission-line and absorption-line spectra explained by quantised atomic energy levels, plus how stellar spectra reveal chemical composition, surface temperature, rotation and radial velocity (Doppler shift).

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Analyse the photoelectric effect, including Einstein's photon equation hf = phi + K_max, the role of Planck's constant, and the inability of the wave model to explain the threshold frequency and the kinetic-energy results

Quantum model of light. Photon energy E = hf, Einstein's photoelectric equation hf = phi + K_max, Planck's constant, threshold frequency and stopping voltage, and why the wave model cannot explain the observations.

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Inquiry Question 3: What evidence supports the relativistic model of the universe?

Compare classical and relativistic momentum, derive p = gamma m v, and analyse the role of relativistic momentum in particle accelerators

Relativistic momentum. Why p = mv fails near c, the relativistic form p = gamma m v, the relativistic energy-momentum relation E^2 = (pc)^2 + (mc^2)^2, and how this drives the design of particle accelerators.

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Derive and apply the mass-energy equivalence E = mc^2, including the calculation of mass defect and binding energy in nuclear reactions

Mass-energy equivalence. The total relativistic energy E = gamma m c^2, the rest energy E_0 = mc^2, mass defect Delta m in nuclear binding, and worked examples for fission, fusion and the deuteron binding energy.

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Investigate experimental and observational evidence for special relativity, including atmospheric and accelerator muon decay, GPS clock corrections, and the routine use of relativistic mechanics in particle physics

Evidence for special relativity. Atmospheric muon flux at sea level, accelerator muon lifetimes, the daily GPS clock corrections (combined SR and GR), and the routine use of relativistic mechanics in particle physics.

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Analyse the Michelson-Morley experiment, state Einstein's two postulates of special relativity, and apply the consequences of time dilation, length contraction and relativity of simultaneity

Light and special relativity. The Michelson-Morley null result, Einstein's two postulates, and quantitative application of time dilation t = gamma t_0, length contraction L = L_0 / gamma and relativity of simultaneity.

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