These Higher Level Physics topics consistently produce the lowest scores. Prioritise these in your revision.
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Microscopic explanations — thermal conduction, resistance at atomic level, entropy
'Describing mechanisms in microscopic terms, as in conduction in solids' was consistently one of the most difficult areas. Students can calculate but struggle to explain the underlying physics in terms of particle behaviour.
Affects: Paper 2
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Nuclear physics — half-life definitions, mass defect, binding energy calculations
'A correct definition for half life was rarely seen.' 'A correct calculation of energy available per kilogram for a nuclear fuel was similarly rarely seen.' Students confuse mass with number of nuclei in half-life.
Affects: Paper 2
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Photoelectric effect — threshold frequency, work function, stopping potential
'The Photoelectric Effect in general seemed poorly understood.' Students confuse work function with kinetic energy. Few could explain why below-threshold light produces no electrons regardless of intensity.
Affects: Paper 2
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Coherence and interference conditions
'Even with a generous marking scheme, clearly there are problems with the understanding of coherence.' Students struggle to explain why coherent sources are needed for sustained interference patterns.
Affects: Paper 2
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Internal resistance and EMF — terminal p.d. vs EMF
'The concept of internal resistance and work having to be done to drive current through a cell seemed particularly problematic.' Students cannot distinguish between EMF and terminal p.d., or explain why terminal p.d. decreases with current.
Affects: Paper 2
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Relativity — spacetime diagrams, simultaneity, length contraction (HL)
'Solving problems on simultaneity' and 'Representing more than one inertial reference frame on the same spacetime diagram' flagged as difficult. Only the best candidates could handle spacetime coordinate transformations.
Affects: Paper 2
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Capacitor smoothing in full-wave rectification (HL)
'It was rare for candidates to score full marks when attempting to discuss the concept of capacitor smoothing in a full wave rectification circuit.' Students know the capacitor smooths but cannot explain the charge/discharge mechanism.
Affects: Paper 2
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Doppler effect for light — identifying and applying in unfamiliar contexts
'Less than half the students identified the Doppler effect' when not explicitly named in the question. Students can calculate Doppler shifts when told to, but fail to recognise when it applies.
Affects: Paper 2