Long answer·Standard multi-step (3/5)·No calculator
Difficulty guide
The label describes the problem, not your ability.
1/5 - Foundational
Warm-up setup; checks one basic idea.
2/5 - Routine exam skill
Normal syllabus skill; usually one main rule or interpretation.
3/5 - Standard multi-step
Exam-style problem with multiple steps or a common trap.
4/5 - Hard exam skill
High-end exam problem; combines methods carefully.
5/5 - Challenge
Stretch problem beyond normal exam pressure.
Question
State Bohr's main postulates for the hydrogen atom and use them to explain why atomic spectra are discrete.
Total: 5 marks
(a) State the postulate about stationary orbits. (2 marks)
(b) State the angular-momentum quantisation condition. (1 mark)
(c) Explain the origin of a spectral line. (2 marks)
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