A-LevelPhysicsQuantum physics9702/41 · May/June 2021 · Q128 Marks
Electromagnetic radiation of a single constant frequency is incident on a metal surface. This causes an electron to be emitted. Explain why the maximum kinetic energy of the electron is independent of the intensity of the incident radiation.
- (a)Electromagnetic radiation of a single constant frequency is incident on a metal surface. This causes an electron to be emitted. Explain why the maximum kinetic energy of the electron is independent of the intensity of the incident radiation.[3]
- (b)Ultraviolet radiation of wavelength 250 nm is incident on the surface of a sheet of zinc. The maximum kinetic energy of the emitted electrons is 1.4 eV. Determine, in eV:
- (b)(i)the energy of a photon of the ultraviolet radiation energy = .............................................................. eV [3][3]
- (b)(ii)the work function energy of the surface of the zinc. energy = .............................................................. eV [2][2]
Mark scheme
Marking points from the official mark scheme (May/June 2021). The mark or mark type is shown in brackets.
- [1] (a) frequency determines energy of photon
- [1] intensity determines number of photons (per unit time)
- [1] intensity does not determine energy of a photon
- [1] kinetic energy (of the electron) depends on the energy of one photon
- [1] (b)(i) E = hc / λ
- [1] E = hf and c = fλ
- [1] E = (6.63 × 10^-34 × 3.00 × 10^8) / (250 × 10^-9)
- [1] (= 7.96 × 10^-19 J)
- [1] = 5.0 eV
- [1] (b)(ii) E_MAX = photon energy – work function
- [1] work function = 5.0 – 1.4
- [1] = 3.6 eV
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