Unit 4: How have creative ideas and investigation revolutionised thinking in physics?

Electromagnetic waves and the EM spectrum. Describes EM waves as transverse oscillations of E and B fields, gives the order-of-magnitude regions of the spectrum (radio, microwave, IR, visible, UV, X-ray, gamma), and applies $c = f \lambda$ across regions.

Proper length as the length measured in the frame where an object is at rest, the length contraction equation L = L0 / gamma, which dimension contracts, and worked examples that tie length contraction to time dilation in a journey between two points.

Proper time as the interval between two events at the same place in a frame, the Lorentz factor, and the time dilation equation t = gamma t0, with a light-clock derivation and worked examples including finding the speed from a measured dilation.

Atomic energy levels. Discrete quantised energy levels, photon emission and absorption with $\Delta E = h f$, line emission spectra, line absorption spectra, and the Bohr-model picture for hydrogen with the Rydberg formula context.

Three applications of special relativity named in the VCE study design. Muons surviving to Earth explained by time dilation and by length contraction, why accelerator lengths must allow for contraction, and why GPS satellite clocks need a speed correction, with worked calculations.

Matter waves. Defines the de Broglie wavelength $\lambda = h / p$, computes electron and other-particle wavelengths, explains the Davisson-Germer experiment as evidence for matter-wave diffraction, and treats the connection to electron microscopy.

The two postulates of Einstein's special theory of relativity, why they differ from classical (Galilean) thinking, inertial frames of reference, and how the null result of the Michelson-Morley experiment supports the theory. A starting point for time dilation and length contraction.

Wave model of light. Covers Young's double-slit experiment, the path-difference condition for constructive and destructive interference, the fringe-spacing formula $\Delta x = \lambda L / d$ in the small-angle limit, and single-slit diffraction.

An extension topic, not in the VCAA key knowledge for Units 3 and 4. Defines polarised and unpolarised light, explains why polarisation requires a transverse-wave nature, applies Malus's law $I = I_0 \cos^2 \theta$, and works through both the unpolarised-to-polariser and polariser-to-second-polariser cases.

Rest energy E0 = mc^2, total energy E = gamma m c^2, relativistic kinetic energy (gamma - 1) m c^2, and how to apply them to the Sun, positron-electron annihilation and particle accelerators, with worked numerical examples in joules and electron-volts.

Photoelectric effect. Sets out the photon energy $E = hf$, the photoelectric equation $E_{k,\max} = hf - \phi$, the role of the work function, the stopping voltage, and the four observations that the classical wave model cannot explain.

Wave-particle duality. Brings together the wave and particle evidence for light (interference vs photoelectric) and matter (Newtonian motion vs electron diffraction), and explains the modern resolution that both light and matter are quantum objects with context-dependent behaviour.

Refraction, which is Unit 1 key knowledge kept at its Unit 4 address. Snell's law, refractive index, the critical angle for total internal reflection, and dispersion as the frequency dependence of refractive index. Includes worked examples and the fibre-optics context.

VCE Physics Unit 4 student-designed investigation (Area of Study 2). Covers research question formulation, variables, design and procedure, logbook entries, raw and processed data, uncertainty propagation, linearised graphs, and the structure of the scientific poster (600-word limit).