Edexcel International A Level Physics Waves and the Particle Nature of Light Exam Questions

About Edexcel International A Level Physics Waves and the Particle Nature of Light

Waves and the particle nature of light is part of Unit 2: Waves and Electricity in Edexcel International A Level Physics. It describes progressive and stationary waves, superposition, refraction, total internal reflection, polarisation, diffraction and the diffraction grating. The second part introduces photons, the photoelectric effect, line spectra and energy levels, and electron diffraction as evidence for wave-particle duality. The topic links back to ideas of energy and forward to nuclear and particle physics in Unit 4. Examiners regularly ask for explanations of why the photoelectric effect supports a particle model of light and for grating and refraction calculations.

What you need to know

• Wave basics v = fλ. Transverse and longitudinal waves; phase difference, path difference and amplitude. Pulse-echo techniques measure distance from the time for a reflected pulse to return.
• Stationary waves Produced when two waves of the same frequency travelling in opposite directions superpose. On a string, v = √(T/μ); nodes are λ/2 apart.
• Refraction n = c/v, n1 sin θ1 = n2 sin θ2 and critical angle sin C = 1/n for light passing into air.
• Polarisation and diffraction Only transverse waves can be polarised. A diffraction grating gives maxima at nλ = d sin θ.
• Photons and the photoelectric effect E = hf. hf = φ + ½mvmax^2, where φ is the work function. Threshold frequency f0 = φ/h.
• Energy levels and duality Line spectra arise from transitions between discrete energy levels: hf = E1 - E2. Electron diffraction shows electrons have wave properties with λ = h/p.

Common mistakes in Waves and the Particle Nature of Light

• Saying increasing intensity increases maximum kinetic energy of photoelectrons. It increases the number emitted per second.
• Forgetting to convert between eV and J.
• Reading wavelength from a displacement-time graph instead of a displacement-distance graph.
• Using lines per mm directly as d in the grating equation.
• Applying total internal reflection when light travels from a less dense to a more dense medium. It only occurs going into a medium of lower refractive index.

Try three Waves and the Particle Nature of Light exam-style questions