Questions on the Photoelectric Effect
Q4.
The graph shows how the maximum kinetic energy, Ek, of electrons emitted from the surface of metal A, varies with the frequency, f, of the incident electromagnetic radiation.
(a) Explain the meaning of the term threshold frequency.
The threshold frequency is the minimum frequency (of radiation) 
required to eject photoelectrons
(2 marks)
(b) Calculate the work function of metal A,
(i) in J,
Φ = hf0 = 6.63 × 10–34 × 4.85 × 1014
Φ = 3.22 × 10–19 J
(ii) in eV.
Φ = 3.22 × 10–19 /1.6 x 10-19 eV
Φ = 2.01 eV
(3 marks)
(c) Metal A is exchanged for metal B. The work function of metal B is half that of metal A. Add a line to the graph above to show how the maximum kinetic energy of electrons emitted from metal B varies with frequency.
see graph - line parallel to the given line with half the value of the x- intercept
(2 marks)
(d) At a fixed frequency of the incident radiation, the emitted electrons are collected and a current is recorded. State and explain a change that may be made to increase this current. You may be awarded marks for the quality of written communication in your answer.
statement :
To increase the current you must increase the light intensity or brightness of the light.
explanation :
Increased intensity will result in more photons per second being incident on the metal.
One photon interacts with one electron and the increase in number of photons incident on the surface willresult in more emitted electrons per second - therefore a greater rate of flow charge (2 max)
(3 marks)
(Total 10 marks)
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