E.2.7 (HL)—Compton scattering
- Syllabus
- First assessment 2025
- Objective
- —
- Level
- HL
Interpret Compton Scattering
HL onlyModel the collision
In Compton scattering, a photon transfers energy and momentum to an electron. The scattered photon has a changed direction and wavelength, while the electron recoils.
Use the evidence
The measured wavelength shift is evidence that photons carry momentum as well as energy. A wave-only model does not account for the collision-like transfer in the same way.
Track conservation laws
Analyse the photon–electron event using conservation of energy and momentum. The photon’s lost energy becomes kinetic energy of the recoiling electron, with the remaining photon energy determining its new wavelength.
Common trap
Do not describe Compton scattering as simple reflection. The photon transfers energy and momentum, so its wavelength generally changes.
E.2.7 (HL) Exam Analysis
HL onlyAssessment in practice
1–2 marksHow it is assessed
Questions ask for experimental evidence of photon momentum or calculate the recoiling electron’s kinetic energy from wavelength data.
Command terms
Outline / Calculate
What earns marks
Name Compton scattering and state the transfer of energy and/or momentum; for calculations, subtract final photon energy from initial photon energy.
Watch for
Mentioning only photon energy without momentum transfer or subtracting the wrong photon energies.