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QLDPhysics2024

QCE Physics 2024

Walkthrough of the 2024 QCE physics exam: what it assessed, strategy tips, and the common errors flagged in the official marker report.

Marks
97
Time
180 min
Authority
QCAA
Updated
Open the official PDF Official marking notes
Key fact

This paper was set on the 2019 QCAA syllabus. From the 2026 external assessments the 2025 syllabus applies, so some content and the exam format have changed. It is still useful practice, but check the current QCAA Physics syllabus and QCAA's 2026 key changes before relying on it. The mark and timing figures at the top of this page are a guide based on the 2024 papers (two papers, each with 90 minutes of working time), not QCAA's official structure for every year. Marks and question types vary, so use QCAA's own paper.

What this paper assessed

This QCAA Physics external assessment is sat as more than one paper. It assesses Unit 3 (Gravity and electromagnetism) and Unit 4 (Revolutions in modern physics):

  • Unit 3 - Gravity and motion: projectile motion, gravitational fields and orbital motion (F=GMmr2F = \frac{GMm}{r^2}, Kepler's laws), and electromagnetism - charged particles and current-carrying conductors in magnetic fields (F=qvBF = qvB, F=BIlF = BIl), and electromagnetic induction (Faraday's and Lenz's laws).
  • Unit 4 - Modern physics: special relativity (time dilation, length contraction, mass-energy E=mc2E = mc^2), the quantum nature of light and matter (the photoelectric effect, E=hfE = hf), and the standard model / nuclear physics.

Many items require extracting data from a graph, applying a relationship, then commenting on the limitations of the model. The extended response rewards structured reasoning over volume of writing. The 2024 paper leaned harder on application where the context was unfamiliar but the skill was core.

Structure and timing

QCAA sets the external assessment as more than one paper, and the number of marks, the sections and the question types differ from year to year. Open the official paper for the exact structure of this year; the marks and time shown at the top of this page are a guide only.

  • Pace by marks. Share your working time in proportion to the marks on offer, so a 6-mark item gets about three times the time of a 2-mark item. Flag any multiple choice item that runs long and return to it.
  • Use perusal time. Scan for the data-heavy items and the longest calculations or extended responses so you can plan them early.
  • Subject habits. Set out every calculation on three lines: the relationship, the substituted values with units, and the final answer with units and appropriate significant figures. For graph-based items, mark the gradient and intercept on the page before stating their physical meaning, and keep a few minutes at the end to check units, vector directions and significant figures.

Worked practice questions (exam-style)

Worked example

Question 1 (5 marks): A satellite orbits Earth in a circular orbit of radius 7.0×106 m7.0 \times 10^6\ \text{m}. Calculate its orbital speed. (Take G=6.67×10−11 N m2 kg−2G = 6.67 \times 10^{-11}\ \text{N m}^2\,\text{kg}^{-2}, MEarth=5.97×1024 kgM_{Earth} = 5.97 \times 10^{24}\ \text{kg}.)

For a circular orbit the only force acting is gravity, and that force must supply all of the centripetal acceleration. Setting the two expressions equal lets us solve for the orbital speed.

Step 1: Equate gravitational and centripetal forces

The gravitational force on the satellite is GMmr2\dfrac{GMm}{r^2} and the centripetal force required is mv2r\dfrac{mv^2}{r}. Setting them equal and cancelling the satellite mass mm:

GMmr2=mv2r⇒v=GMr.\frac{GMm}{r^2} = \frac{mv^2}{r} \quad\Rightarrow\quad v = \sqrt{\frac{GM}{r}}.

Step 2: Substitute the known values

Insert G=6.67×10−11 N m2 kg−2G = 6.67\times10^{-11}\ \text{N m}^2\,\text{kg}^{-2}, MEarth=5.97×1024 kgM_{Earth} = 5.97\times10^{24}\ \text{kg}, and r=7.0×106 mr = 7.0\times10^6\ \text{m}:

v=(6.67×10−11)(5.97×1024)7.0×106=3.982×10147.0×106.v = \sqrt{\frac{(6.67\times10^{-11})(5.97\times10^{24})}{7.0\times10^6}} = \sqrt{\frac{3.982\times10^{14}}{7.0\times10^6}}.

Step 3: Evaluate and state the result

v=5.69×107≈7.5×103 m s−1.v = \sqrt{5.69\times10^{7}} \approx 7.5 \times 10^3\ \text{m s}^{-1}.

Final answer: the orbital speed is approximately 7.5×103 m s−17.5 \times 10^3\ \text{m s}^{-1} (7.5 km s−1^{-1}).

Worked example

Question 2 (5 marks): In a photoelectric experiment, light of frequency 7.5×1014 Hz7.5 \times 10^{14}\ \text{Hz} ejects electrons from a metal with work function 2.0 eV2.0\ \text{eV}. Calculate the maximum kinetic energy of the ejected electrons in joules. (Take h=6.63×10−34 J sh = 6.63 \times 10^{-34}\ \text{J s}, 1 eV=1.60×10−19 J1\ \text{eV} = 1.60 \times 10^{-19}\ \text{J}.)

Einstein's photoelectric equation states that the photon energy goes first into freeing the electron (the work function) and any remainder becomes kinetic energy. We calculate each quantity in joules so the units are consistent throughout.

Step 1: Calculate the photon energy in joules

The energy carried by a single photon of frequency ff is E=hfE = hf:

E=(6.63×10−34)(7.5×1014)=4.97×10−19 J.E = (6.63\times10^{-34})(7.5\times10^{14}) = 4.97\times10^{-19}\ \text{J}.

Step 2: Convert the work function to joules

The work function is given in electron-volts, so convert using 1 eV=1.60×10−19 J1\ \text{eV} = 1.60\times10^{-19}\ \text{J}:

W=2.0×1.60×10−19=3.20×10−19 J.W = 2.0 \times 1.60\times10^{-19} = 3.20\times10^{-19}\ \text{J}.

Step 3: Apply Einstein's photoelectric equation

Since hf>Whf > W, electrons are emitted. The maximum kinetic energy is the photon energy minus the work function:

Ek,max⁡=hf−W=4.97×10−19−3.20×10−19=1.77×10−19 J.E_{k,\max} = hf - W = 4.97\times10^{-19} - 3.20\times10^{-19} = 1.77\times10^{-19}\ \text{J}.

Final answer: maximum kinetic energy ≈1.8×10−19 J\approx 1.8 \times 10^{-19}\ \text{J} (about 1.1 eV).

Worked example

Question 3 (5 marks): A muon has a proper lifetime of 2.2 μs2.2\ \mu\text{s} and travels at 0.99c0.99c relative to an observer on Earth. Calculate the lifetime measured by the Earth observer and explain why this allows muons to reach the surface.

Time dilation: t=t01−v2/c2t = \dfrac{t_0}{\sqrt{1 - v^2/c^2}}, with t0=2.2 μst_0 = 2.2\ \mu\text{s} and v=0.99cv = 0.99c.

Lorentz factor: γ=11−0.992=11−0.9801=10.0199≈10.1411≈7.09.\gamma = \dfrac{1}{\sqrt{1 - 0.99^2}} = \dfrac{1}{\sqrt{1 - 0.9801}} = \dfrac{1}{\sqrt{0.0199}} \approx \dfrac{1}{0.1411} \approx 7.09.

Dilated lifetime:

t=γt0=7.09×2.2 μs≈15.6 μs.t = \gamma t_0 = 7.09 \times 2.2\ \mu\text{s} \approx 15.6\ \mu\text{s}.

Explanation: in the muon's frame it lives only 2.2 μs2.2\ \mu\text{s}, which (even at near light speed) would not allow it to reach the ground. But to the Earth observer the muon's "clock" runs slow, so it survives ~15.6 μs - long enough to travel the distance through the atmosphere. (Equivalently, in the muon's frame the atmosphere is length-contracted.)

Common errors students made

The 2024 QCAA marker report flagged that students:

  • omitted units in answers;
  • mixed scalar and vector quantities;
  • treated projectile motion as one-dimensional rather than resolving components;
  • forgot that induced EMF depends on the rate of change of flux, not flux itself.

Further traps to avoid:

  • Inconsistent units - failing to convert eV to J, or μs to s, before substituting.
  • Applying time dilation/length contraction in the wrong reference frame.
  • Using the wrong significant figures - match the precision of the data.
  • Stating a graph trend without quoting gradient/intercept values or their physical meaning.

How to use this paper

  1. The 2024 sitting was two papers of 90 minutes working time each, with 10 minutes of perusal in the booklets. QCAA's 2026 timetable has two papers, each with 5 minutes of perusal and 90 minutes of working time (check the current QCAA syllabus for your sitting). Sit one paper at a time under timed conditions, pacing each by marks. Have your calculator and data sheet ready.
  2. Self-mark against the QCAA marking guide and marker report using the links at the top of this page, awarding method marks line by line.
  3. For each calculation, write the relationship, substitute, then evaluate with units and sig figs.
  4. Rewrite one extended response per session as principle, application to the named scenario, and evaluation of assumptions/limitations.

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