Wave-particle duality — common mistakes

Pay close attention to units, especially when converting between electronvolts (eV) and Joules (J) for energy calculations in the photoelectric effect and atomic energy levels. Remember Planck's constant (h) is given in Js, so ensure your energies are in Joules for calculations using E=hf.

Wave-particle duality is the concept that quantum entities, such as light and electrons, can display both wave-like and particle-like properties depending on how they are observed. It's crucial because it revolutionised classical physics, explaining phenomena unexplainable by either pure wave or pure particle models, and forms the bedrock of quantum mechanics.

The photoelectric effect shows that electron emission from a metal depends on the light's frequency, not its intensity, and only occurs above a threshold frequency. This 'all-or-nothing' behaviour, along with instantaneous emission, strongly supports light consisting of discrete energy packets (photons) that interact one-to-one with electrons, rather than continuous waves.

Yes, according to the de Broglie hypothesis, all matter has an associated de Broglie wavelength. However, for everyday objects like a cricket ball, the mass (m) is so large that its momentum (p=mv) is also very large. Since wavelength λ = h/p, the de Broglie wavelength becomes incredibly tiny – far too small to observe any measurable wave effects like diffraction.