Q21 · 2022 · Paper 1Simple familiar2 marks
QUESTION 21 (2 marks)
A hot iron bar was observed to have a deep red colour. As the iron bar was heated further, the colour changed to orange. Explain the observed colour change in terms of black-body radiation.
WORKED SOLUTION
2 marksQCAA guide · typeset solution
ANSWER
See worked solution below.
Worked solution
The iron bar represents a model of black-body radiation,
where the spectrum of radiation emitted is due to the
conversion of the object’s thermal energy. This is outlined
by Wien’s Law, where 𝜆𝜆𝑚𝑚𝑚𝑚𝑚𝑚=
𝑏𝑏
𝑇𝑇.
As the temperature increases, the peak wavelength will be
shorter and this is observed by the colour change from red
to orange.
• describes the scenario in terms of black-body
radiation [1 mark]
• uses Wien’s Law to explain the colour change in
the iron bar [1 mark]
One QCAA sample method typeset for web; criterion wording is adapted from the official marking guide.
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