Q4 · 2020 · Paper 2Simple familiar5 marks
QUESTION 4 (5 marks)
Describe how experiments on the photoelectric effect provide evidence of the quantised nature of photons.
WORKED SOLUTION
5 marksQCAA guide · typeset solution
ANSWER
See worked solution below.
Worked solution
The photoelectric effect experiment demonstrates that the
number of electrons ejected from a metal plate is
proportional to the intensity of incident light, whereas the
proportional to the intensity of incident light, whereas the
kinetic energy of the ejected electrons is proportional to
the frequency of incident light. The fact that frequencies
lower than a threshold value will not eject an electron
suggests that light energy is quantised. As the frequency
increases, the kinetic energy of the ejected electrons
increases, the kinetic energy of the ejected electrons
increases, suggesting that light can be conceived as
packets of energy (photons). The fact that a greater
intensity of light causes more electrons to be ejected
intensity of light causes more electrons to be ejected
suggests that the greater the intensity, the more photons
(or packets of energy) are incident on the metal plate,
also confirming the idea of light as a photon.
also confirming the idea of light as a photon.
• describes
three relevant features of the
photoelectric effect
two relevant features of the
photoelectric effect
3 marks
2 marks
one relevant feature of the
photoelectric effect
1 mark
• identifies how
two relevant features provide
evidence of quantisation of photons
2 marks
one relevant feature provides
evidence of quantisation of photons
1 mark
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
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