Q271 · Practice questionSimple familiar3 marks
QUESTION 271 (3 marks)
Rutherford extquotesingle s model places a small positive nucleus at the centre of the atom with electrons outside it. Consider an electron modelled as orbiting classically.
a)[3 marks]
Explain one stability problem for this classical orbit model, and explain how Bohr extquotesingle s model accounts for stable atoms and discrete emission wavelengths.
WORKED SOLUTION
3 marksPractice marking scheme
ANSWER
(a) A classically accelerating electron would radiate energy and spiral inward. Bohr postulated nonradiating stationary states and photon emission only for transitions between allowed energies.
Worked solution
(a) Circular orbital acceleration would produce radiation under classical electromagnetism, causing energy loss and orbital collapse. Bohr allowed discrete stationary states that do not radiate. A transition emits a photon with , so discrete energy differences give discrete wavelengths.
Equivalent physically justified methods, alternative valid sketches and consistent units accepted.
Accept sensible significant figures and consistent rounding from stated constants.
Part a: Connect classical acceleration/radiation with energy loss and instability.
Part a: State the nonradiating discrete stationary states.
Part a: Link discrete energy differences to photon energies and spectral lines.
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