Q8 · 2021 · Paper 2Simple familiar4 marks
QUESTION 8 (4 marks)
A photoelectric effect experiment was conducted by shining light from a laser at one frequency on five different metals with known work functions. The graph shows the maximum kinetic energy of the photoelectrons ejected from each metal with respect to their work functions.
Determine the wavelength of the light emitted by the laser.
WORKED SOLUTION
4 marksQCAA guide · typeset solution
ANSWER
See worked solution below.
Worked solution
𝐸𝑘= ℎ𝑓−𝑊
𝐸𝑘= −𝑊+ ℎ𝑓
The y-intercept of the line will be ℎ𝑓
𝑦= 𝑚𝑥+ 𝑐
To determine the gradient, the data (6, 2) and (8, 0) were
used
𝑚= 𝑦2 −𝑦1
𝑥2 −𝑥1
= 0 −2
8 −6
= −1
Therefore 𝑦= −1𝑥+ 𝑐
Substitute (8, 0)
0 = −1 × 8 + 𝑐
𝑐= 8
Therefore
ℎ𝑓= 𝑐
𝑓= 𝑐
ℎ
=
8 × 10−19
6.626 × 10−34
≈1.2 × 1015 Hz
Wavelength = 248 nm (to the nearest whole number)
• recognises the scenario relates to 𝐸𝑘= ℎ𝑓−𝑊
[1 mark]
• uses appropriate features of the graph to
determine a value for ℎ𝑓 [1 mark]
• provides correct reasoning [1 mark]
• determines wavelength [1 mark]
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
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