A-LevelPhysicsQuantum physics9702/42 · Oct/Nov 2021 · Q99 Marks
A polished calcium plate in a vacuum is investigated by illuminating the surface with light. It is found that no photoelectric current is produced when the frequency of the light is less than 6.93 x 10¹⁴ Hz.
- (a)(i)State what is meant by: the photoelectric effect[2]
- (a)(ii)State what is meant by: work function energy.[1]
- (b)(i)State the name of the frequency below which no photoelectric current is produced.[1]
- (b)(ii)Explain how the photon model of electromagnetic radiation accounts for this phenomenon.[3]
- (b)(iii)Calculate the work function energy, in eV, of calcium.[2]
Mark scheme
Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.
- emission of electrons (from a metal surface)
- when electromagnetic radiation is incident (on electrons)
- minimum energy required for an electron to leave surface
- threshold (frequency)
- photons are (discrete) packets of energy
- energy of photons depends on frequency (of EM radiation)
- electrons can only absorb a single photon (of energy)
- emission only possible if photon energy is at least the work function
- work function = hfo = 6.63 x 10-34 × 6.93 × 1014
- = 4.59 × 10-19 (J)
- = 4.59 × 10-19 / 1.60 × 10–19 (eV)
- = 2.87 eV
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