Wave Particle Duality

Overview

This lesson brings together the evidence that light and matter cannot be described using only one classical model. You will compare photon evidence from the photoelectric effect with wave evidence from interference, diffraction, and electron diffraction.

What You Need to Know

• The photoelectric effect provides evidence for the particulate nature of electromagnetic radiation.
• Interference and diffraction provide evidence for the wave nature of electromagnetic radiation.
• Electron diffraction shows that moving particles can display wave behaviour.
• The de Broglie wavelength is the wavelength associated with a moving particle.
• For a particle, lambda = h / p, so larger momentum means a shorter de Broglie wavelength.

How to Work Through It

1. Start by sorting evidence into wave evidence and particle evidence.
2. Interpret the pattern from electron diffraction qualitatively.
3. Define de Broglie wavelength and connect it to momentum.
4. Practise calculations using lambda = h / p and explain what the answer means physically.

Check Your Understanding

• Which observations support a photon model of electromagnetic radiation?
• Why does electron diffraction challenge a purely particle-only model of electrons?
• What happens to de Broglie wavelength when particle momentum increases?
• Why are wave effects harder to observe for everyday objects?

Common Mistakes

• Saying light is sometimes a wave and sometimes a particle without linking each model to evidence.
• Treating electron diffraction as electrons bouncing off atoms rather than producing a diffraction pattern.
• Forgetting that momentum, not mass alone, sets the de Broglie wavelength.
• Using frequency equations for a particle when lambda = h / p is required.

Next Steps

• Consolidate the nuclear and quantum equations before revision.
• Be ready to explain evidence in words, not only complete calculations.