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LearnCambridge97022025–2027Paper 2 · AS Level Structured QuestionsSuperposition

Paper 2 · Module

Superposition

3 subtopics≈ 115 min in total

Start the module: Stationary waves Open graphing calculator

Stationary waves
When two identical progressive waves travel in opposite directions, they superpose to form a stationary wave. Nodes (zero amplitude) and antinodes (maximum amplitude) stay in fixed places, $\tfrac\lambda2$ apart. No energy is carried along. On a string fixed at both ends the fundamental has $\lambda=2L$ ; in a pipe closed at one end, $\lambda=4L$ .
≈ 40 min
Diffraction and interference
Waves spread out (diffract) through gaps about the size of their wavelength. Two coherent sources produce an interference pattern: bright fringes where the path difference is a whole number of wavelengths, dark fringes where it's a half-integer. For Young's double slits, fringe spacing $x=\dfrac{\lambda D}a$ .
≈ 40 min
The diffraction grating
A diffraction grating has thousands of equally spaced slits. Maxima appear only at angles where light from every slit arrives in phase: $d\sin\theta=n\lambda$ , with $d$ the slit spacing. The maxima are much sharper and brighter than with two slits, so gratings measure wavelengths precisely and split light into spectra.
≈ 35 min