Photons and the photoelectric effectEdexcel A-Level Physics: Flashcards

Exam questions on Photons and the photoelectric effect

1. A clean zinc plate is fixed to a gold-leaf electroscope that has been given a negative charge. When ultraviolet radiation shines on the plate, the gold leaf slowly falls. When bright visible light shines on the plate, the leaf does not fall, however long it is left. The work function of zinc is 4.3 eV.
   Use the photon model to explain why increasing the intensity of the visible light does not make the leaf fall.2 marks
2. Caesium has a work function of 2.1 eV. A clean caesium surface in an evacuated cell is illuminated with monochromatic light of wavelength 450 nm, and photoelectrons are emitted.
   Calculate the maximum speed of the photoelectrons emitted. (Electron mass = 9.11 × 10⁻³¹ kg; use the photon energy from part (a).)2 marks
3. A student illuminates a clean metal surface with radiation of different frequencies and measures the maximum kinetic energy of the emitted photoelectrons. At a frequency of 7.0 × 10¹⁴ Hz the maximum kinetic energy is 1.44 × 10⁻¹⁹ J, and at 10.0 × 10¹⁴ Hz it is 3.43 × 10⁻¹⁹ J.
   Use the two sets of results to determine a value for the Planck constant.3 marks