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Wave frequency and photon energy Motion graphs and wave graphs: read the axes Refraction changes speed and wavelength together Path difference becomes phase difference Stationary waves are a superposition pattern Use a stationary pattern to measure wave speed Diffraction connects electrons with other waves Waves4.4 Quantum physics4.5 Kinematics3.1.1 Wave motion4.4.1 Electromagnetic waves4.4.2 Superposition4.4.3 Stationary waves4.4.4 Wave–particle duality4.5.3
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Physics connection

Path difference becomes phase difference

OCR A AS Physics · Two ideas, one explanation

Two coherent waves can reinforce or cancel because their displacements add. Path difference determines their phase relationship at the observation point.

One wavelength of path difference = 2π phase difference

Follow the reasoning

  1. Check that the sources have a stable phase relationship.
  2. Express the path difference as a fraction of wavelength.
  3. Add the displacements with their phases.
Specification outcomes (4)
  • 4.4.1(b)(i) Define displacement, amplitude, wavelength, period, phase difference, frequency and speed of a wave.
  • 4.4.1(e) Interpret graphs of transverse and longitudinal waves.
  • 4.4.3(c) Define and describe interference, coherence, path difference and phase difference.
  • 4.4.3(d) Explain constructive and destructive interference in terms of path and phase difference.
Open the official OCR AS specification ↗

H156 v2.0 · May 2026

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