A-LevelPhysicsQuantum physics9702/42 · Feb/Mar 2019 · Q119 Marks
State what is meant by a photon.
- (a)State what is meant by a photon.[2]
- (b)Calculate the energy, in eV, of a photon of light of wavelength 540 nm.[3]
- (c)The outermost electron energy bands of a semiconductor material are illustrated in Fig. 11.1. The width of the forbidden band is 1.1 eV. Explain why, when photons of light, each of energy 2.1 eV, are incident on the semiconductor material, its resistance decreases. [Figure 11.1][4]
This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.
Mark scheme
Marking points from the official mark scheme (Feb/Mar 2019). The mark or mark type is shown in brackets.
- [M1] quantum / packet / discrete amount of energy
- [A1] of electromagnetic radiation
- [C1] E = hc / λ
- [C1] = (6.63 × 10⁻³⁴ × 3.0 × 10⁸) / (540 × 10⁻⁹)
- [A1] = (3.68 × 10⁻¹⁹) / (1.6 × 10⁻¹⁹) = 2.3 eV
- [B4] Any 4 from: photon absorbed by electron in valence band (1); photon energy > energy of forbidden band (1); electron promoted to conduction band (1); hole left in valence band (1); more charge carriers so lower resistance (1)
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