Paper 3 Wave-Particle Duality Drills

Q1 Comparing Light and Electrons

1. Explain how light shows particle-like behaviour in the photoelectric effect. [3]
2. Explain how electrons show wave-like behaviour in diffraction. [3]
3. Discuss why intensity and frequency must be distinguished when interpreting photon experiments. [3]

Q2 Electron Diffraction

Electrons are accelerated from rest through a p.d. of $220\mathrm{V}$ and are incident normally on a thin crystal. Use $h=6.63\times 10^{-34}\mathrm{J}\mathrm{s}$, $m_e=9.11\times 10^{-31}\mathrm{kg}$ and $e=1.60\times 10^{-19}\mathrm{C}$.

1. Show that the electron de Broglie wavelength is approximately $8.3\times 10^{-11}\mathrm{m}$. [4]
2. Adjacent crystal planes have spacing $d=2.00\times 10^{-10}\mathrm{m}$. Using the first-order condition $d\sin \theta =\lambda$, calculate $\theta$. [2]
3. State and explain how $\theta$ changes when the accelerating p.d. is increased. [3]
4. Explain why the diffraction pattern is evidence for wave behaviour but the detector still records localised electron arrivals. [3]