Practice question · Sort into groups
Sort each observation by whether the classical wave picture can account for it.
Groups: Explained by waves alone · Requires photons
- A glowing gas showing only a few discrete wavelengths
- A beam bending as it passes into glass
- A sharp threshold frequency for electron ejection
- Interference fringes from a double slit
- A photocurrent that stops dead below a cut-off colour
Hints
- Ask whether the effect depends on energy arriving in indivisible packets.
- Anything involving a sharp energy threshold or discrete levels needs photons.
Show the answer
Explained by waves alone: A beam bending as it passes into glass, Interference fringes from a double slit
Requires photons: A sharp threshold frequency for electron ejection, A glowing gas showing only a few discrete wavelengths, A photocurrent that stops dead below a cut-off colour
Why
Refraction and interference are pure wave behaviour and never needed quantisation. A frequency threshold, discrete spectral lines and instant ejection at low intensity all require energy to arrive in indivisible packets of .
Practise Atomic Spectra and the Quantum Atom
The app has 5 more questions on this lesson, and keeps your place in the course. Chemistry I is free to start.
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