Mark it yourself: HSC Physics calculations and extended responses

How to use this pack

This pack shows how HSC Physics answers are marked for four question types that appear every year. For each type you get the official NESA criteria pattern, quoted from the 2025 HSC Physics marking guidelines, a mark-by-mark breakdown, an original practice question with our own top-band sample answer (written by ExamExplained, not an official NESA exemplar), the errors that cost marks, and a self-marking prompt for an AI tool.

How the Physics marking guidelines work

• Calculations are marked by progress. 2025 Question 28 (4 marks): "Calculates the minimum speed required for the rider to land on the second ramp" (4); "Provides substantial working to calculate the minimum speed" (3); "Makes progress towards determining the minimum speed" (2); "Provides some relevant information" (1).
• Explain questions want the law and the maths. 2025 Question 29(b) (3 marks) needed the comparison made "using the law of conservation of energy" AND "Uses appropriate mathematical relationships". Without the relationships, the same answer earned 2.
• Experimental questions want relationships. 2025 Question 35 (4 marks) rewarded answers that "Relates the measurements on the balance to the motion of the magnet and its interactions with the pipe". Describing what happened without relating it earned 2.
• Extended responses need evidence. 2025 Question 32 (8 marks) asked for "a comprehensive analysis of the consequences of special relativity on time, length and motion" that "Refers to applicable experimental evidence".

NESA's glossary defines the key verbs: explain is "Relate cause and effect. Make the relationships between things evident. Provide why and/or how." Analyse is "Identify components and the relationship between them. Draw out and relate implications."

Type 1: the multi-step calculation (3 to 4 marks)

Practice question (ours). A geostationary satellite orbits Earth once every 24 hours. Calculate its altitude above Earth's surface. (Earth's mass = 6.0 x 10²⁴ kg, Earth's radius = 6.37 x 10⁶ m, G = 6.67 x 10⁻¹¹ N m² kg⁻²) (4 marks)

Our sample answer (full marks).

T = 24 x 3600 = 86 400 s

For a circular orbit, $\dfrac{r^3}{T^2} = \dfrac{GM}{4\pi^2}$, so $r^3 = \dfrac{GMT^2}{4\pi^2}$

$r^3 = \dfrac{(6.67 \times 10^{-11})(6.0 \times 10^{24})(86\,400)^2}{4\pi^2} = 7.57 \times 10^{22}$ m³

$r = \sqrt[3]{7.57 \times 10^{22}} = 4.23 \times 10^{7}$ m (radius of orbit, from Earth's centre)

Altitude = r minus Earth's radius = 4.23 x 10⁷ - 0.637 x 10⁷ = 3.6 x 10⁷ m

Other common mark-losing errors: leaving T in hours; squaring instead of cubing r; quoting ten significant figures; no units on the final answer.

Type 2: explain using a law and a relationship (3 marks)

Practice question (ours). Explain why the current in a DC motor is largest when it is first switched on and decreases as the motor speeds up. (3 marks)

Our sample answer (full marks).

When the motor is switched on, the coil is not yet rotating, so there is no change in flux through it and no induced emf. The current is limited only by the coil's small resistance, I = V/R, so it is large.

As the coil rotates in the magnetic field, the flux through it changes, so by Faraday's law an emf is induced ($\varepsilon = -N\frac{\Delta\Phi}{\Delta t}$). By Lenz's law this back emf opposes the supply voltage that is causing the rotation. The net voltage driving current is the supply voltage minus the back emf, so $I = \dfrac{V - \varepsilon}{R}$.

The faster the coil rotates, the greater the rate of change of flux, so the larger the back emf and the smaller the current. At a steady speed the current is just large enough to provide the torque needed to overcome friction and the load.

Other common mark-losing errors: saying the resistance of the coil increases with speed; confusing the motor effect (force on a current) with induction (emf from changing flux); no equation.

Type 3: relating experimental results to a model (3 to 4 marks)

Practice question (ours). In the Geiger-Marsden experiment, alpha particles were fired at a thin gold foil. Explain how the results led Rutherford to propose his model of the atom. (4 marks)

Our sample answer (full marks).

Most alpha particles passed straight through the foil with little or no deflection. This showed that most of the atom is empty space, because the alpha particles met nothing that could exert a large force on them.

A small fraction were deflected through large angles, and a very small number (about 1 in 8000 in Geiger and Marsden's measurements) bounced back through more than 90°. Alpha particles are positive and relatively massive, so turning them back requires a very strong repulsive force. This showed that the atom's positive charge and almost all of its mass are concentrated in a tiny central region, the nucleus.

Thomson's model, with positive charge spread through the whole atom, could not produce forces strong enough to cause these large deflections. Rutherford therefore proposed a small, dense, positive nucleus with electrons orbiting in the mostly empty space around it.

Other common mark-losing errors: saying the alpha particles "hit" electrons; forgetting that the alpha particles are positive (which is why repulsion matters); not saying why Thomson's model fails.

Type 4: the 6 to 8 mark "analyse" question

Official pattern (2025, Question 33, 6 marks): "Provides a detailed analysis of how experimental evidence and theoretical ideas contributed to the development of the Standard Model of matter" (6); "Provides an analysis of ..." (5); "Describes experiment(s) and idea(s) relating to fundamental particles and/or forces AND links these to the Standard Model of matter" (3 to 4); "Outlines experiments and/or ideas" (2); relevant information (1). Question 32 (8 marks) used "comprehensive" (8), "thorough" (6 to 7) and required answers that refer "to applicable experimental evidence".

Practice question (ours). Analyse how observational evidence and theoretical ideas support the Big Bang theory. (6 marks)

Our sample answer (top band).

The Big Bang theory states that the universe began in an extremely hot, dense state about 13.8 billion years ago and has been expanding and cooling ever since. Its acceptance came from theory predicting features of the universe that observations then confirmed.

Theory came first. Solutions of Einstein's general relativity found by Friedmann and Lemaître in the 1920s showed that the universe could not be static: it must be expanding or contracting. Lemaître proposed that an expanding universe began from a very dense initial state.

Hubble's observations (1929) of galaxies showed that their spectral lines are redshifted, and that the redshift increases in proportion to distance ($v = H_0 d$). The simplest interpretation is that space is expanding, carrying galaxies apart. Running the expansion backwards implies that everything was once much closer together, which supports a hot, dense beginning rather than a static universe.

The theory predicted that the early universe was filled with radiation that would now be redshifted to microwave wavelengths. In 1965 Penzias and Wilson detected cosmic microwave background radiation arriving almost uniformly from every direction, with a black-body spectrum at about 2.7 K. This is strong evidence, because the rival steady state theory could not explain a uniform black-body background, and it was a prediction made before the discovery.

The theory also predicts, from nuclear fusion in the first few minutes, that ordinary matter should be about 75% hydrogen and 25% helium by mass, with traces of deuterium and lithium. Spectroscopic measurements of the oldest stars and gas clouds match these proportions, which supports the hot early phase.

Taken together, the theoretical predictions (expansion, a background of relic radiation, light-element abundances) and three independent lines of observational evidence reinforce each other, which is why the Big Bang theory is the accepted model of the universe's origin.

Why it reaches the top band: every piece of evidence is named and dated where relevant, each is linked to what it shows, the role of theory (prediction before observation) is analysed, and the conclusion draws the relationships together.

The errors that cost the most marks in 6 to 8 mark questions:

• A list of facts with no analysis. "Hubble found redshift. The CMB was discovered." with no statement of what each shows reads as an outline (2 marks).
• Evidence without theory, or theory without evidence. The criteria name both.
• Vague evidence. "Scientists found radiation" is weaker than naming the CMB, its temperature and why it matters.
• Describing the Big Bang as an explosion into space. It is an expansion OF space.

Your self-marking prompt

Paste this into NSWEduChat, ChatGPT or another AI tool, with the criteria for the matching type above (or the official criteria for a past-paper question).

You are an experienced HSC Physics marker. Mark my answer strictly against
the marking criteria below. Do not award a mark the criteria do not allow,
and do not reward length.

Question ([number] marks): [paste the question and any data]

Marking criteria:
[paste the criteria, one line per mark level]

My answer:
[paste your answer with all working]

1. Solve the question yourself first and show the correct answer or the
   key points a top answer needs.
2. Go through my working line by line. Say where the first error is, if
   there is one, and whether later steps follow correctly from it.
3. For each criterion, quote the words in my answer that meet it, or say
   that it is not met (for example: no relationship, no evidence named,
   observation not linked to the model).
4. Give my mark, name the criteria level, and tell me the one change that
   would earn the next mark. Do not rewrite my whole answer.

Next steps

• Practise Section I with the harder exam-style HSC Physics quiz.
• Revise the physics behind these answers in the mechanics and electromagnetism guide and the light and quantum guide.
• Then write a full NESA past paper under time and mark it with that year's official guideline.