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A2 · Topic 25

Measuring the Universe.

The luminosity of a star and the inverse square law, the colour that betrays its temperature through Wien and Stefan-Boltzmann, and the redshift that reveals an expanding Universe and Hubble's law. The most ambitious topic in the syllabus, where a faint smudge of light becomes a distance, a size, and an age. Play the three simulations below. The gamified lessons and the topic Paper 4 practice are live below too.

Simulations · live
Interactive · live Inverse square law and standard candles Move the detector and watch the flux collapse as F = L / (4πd²): double the distance, quarter the flux. Loads only when you launch, so the page stays fast.
Interactive · live Black-body spectrum: Wien and Stefan-Boltzmann Drag the temperature and watch the peak slide blue while the whole curve climbs; combine L and T for the radius. Loads only when you launch, so the page stays fast.
Interactive · live Redshift and Hubble's law Send a galaxy farther away and watch its line slide red as the recession speed climbs the v = H₀d line. Loads only when you launch, so the page stays fast.
Paper 4 practice · live
Structured questions · with worked solutions Ten original Paper 4 style questions A full topic set across standard candles, stellar radii and Hubble's law, linking the lessons with full worked solutions. Open practice →
Lessons · live
Standard candles and the inverse square law → Stellar radii: Wien and Stefan-Boltzmann → Hubble's law and the Big Bang →
Concept map
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