Quick answer: Light comes in photons of energy E = hf. In the photoelectric effect a photon ejects an electron only if hf is at least the work function φ, and the electron then has maximum kinetic energy Kmax = hf − φ. This Physics 11-12 test on photoelectric effect has 8 questions worth 20 marks, to do in 45 minutes: photon energy, work function and einstein’s equation. The mark scheme is on a separate page; free printable PDF.
This test covers photon energy, the photoelectric effect, graph analysis and de Broglie wavelength. Show formulas, substitutions and units. Use h = 6.63 × 10⁻³⁴ J s, c = 3.00 × 10⁸ m/s, e = 1.60 × 10⁻¹⁹ C and electron mass 9.11 × 10⁻³¹ kg.
Level: Physics grades 11-12 (A Level · IB · Class 11-12) · Curriculum: IB E.2
Question 1 Photon energy (2 marks)
Calculate the energy of a photon of frequency 7.5 × 10¹⁴ Hz.
Question 2 Work function (2 marks)
Define work function and threshold frequency, and state how they are related.
Question 3 Einstein’s equation (3 marks)
The work function of a metal is 2.1 eV. Light of wavelength 450 nm falls on it. Calculate the maximum kinetic energy of the photoelectrons in eV and the stopping potential.
Question 4 Wave model failure (3 marks)
Explain why the wave model of light cannot explain why no electrons are emitted from a metal by bright light below the threshold frequency.
Question 5 Intensity (2 marks)
The intensity of light above threshold is halved. State the effect on the photocurrent and on Kmax.
Question 6 Graph analysis (3 marks)
The graph shows Kmax against frequency for a metal.
- Read the threshold frequency. (1 mark)
- Calculate the work function in eV. (2 marks)
Question 7 de Broglie (3 marks)
Calculate the de Broglie wavelength of an electron moving at 4.0 × 10⁶ m/s.
Question 8 Duality evidence (2 marks)
Name one experiment that shows the particle nature of light and one that shows the wave nature of electrons.
