Cambridge International AS & A Level · 22 · structured
A photon can carry energy and momentum
A photon can carry energy and momentum · Original GioPhysics question with a detailed, mark-by-mark answer guide.
- Demand
- demanding
- Marks
- 4
- Topics
- 2
- Answer
- Complete
A single photon has energy 3.30×10⁻¹⁹ J and travels in the +x direction in vacuum. Use c=3.00×10⁸ m s⁻¹.
- (a)
Explain what is meant by a photon as a quantum of electromagnetic energy.
2 marks - (b)
Use the photon energy–momentum relation to calculate its momentum. Give the momentum transferred to a stationary absorber that absorbs this photon completely.
2 marks
Ready to self-mark?Reveal the detailed answer guide
(a)
Explain what is meant by a photon as a quantum of electromagnetic energy.
Identify what the question is testing, organise the response into distinct mark-earning points, and make every conclusion traceable to a physical principle or to the evidence supplied.
- 1
Electromagnetic energy is emitted or absorbed in discrete quanta called photons.
- 2
A photon at frequency f carries energy hf; it is not an arbitrary continuously divisible share in one interaction.
(b)
Use the photon energy–momentum relation to calculate its momentum. Give the momentum transferred to a stationary absorber that absorbs this photon completely.
List the given quantities with units, identify the required quantity, write the governing relationship before substituting, and keep extra digits until the final line so rounding does not distort the result.
- 1
For a photon p=E/c, not a nonrelativistic massive-particle kinetic-energy formula.
- 2
p=3.30×10⁻¹⁹/(3.00×10⁸)=1.10×10⁻²⁷ kg m s⁻¹; by momentum conservation complete absorption transfers this in +x.
Complete marking guidance
Use these worked steps alongside the part-by-part answers. They explain the method and mark allocation; they do not add extra marks.
- (a) Electromagnetic energy is emitted or absorbed in discrete quanta called photons.
- (a) A photon at frequency f carries energy hf; it is not an arbitrary continuously divisible share in one interaction.
- (b) For a photon p=E/c, not a nonrelativistic massive-particle kinetic-energy formula.
- (b) p=3.30×10⁻¹⁹/(3.00×10⁸)=1.10×10⁻²⁷ kg m s⁻¹; by momentum conservation complete absorption transfers this in +x.
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