§-Past paper

VICPhysics2021

VCE Physics 2021

Walkthrough of the 2021 VCE physics exam: what it assessed, strategy tips, and the common errors flagged in the official marker report.

Marks: 130
Time: 150 min
Authority: VCAA
Updated: 2026-05-29

Open the official PDF ->Official marking notes

What this paper assessed

The VCAA Physics Units 3 & 4 examination (130 marks in 150 minutes) covers:

Unit 3 - How do fields explain motion and electricity: gravitational, electric and magnetic fields; motion in fields (projectiles, satellites, circular motion); electric power generation and transmission (electromagnetic induction, transformers, AC).
Unit 4 - How can two contrasting models of light and matter be reconciled / How is scientific inquiry used: the wave and particle models of light, the photoelectric effect, matter waves, special relativity (time dilation, length contraction, $E = mc^2$ ), and the analysis of motion and momentum.

The exam combines multiple choice with short and extended response. Many items required extracting data from a graph, applying a relationship, then commenting on assumptions or the limits of a model. Markers rewarded the relationship, substitution and unit-bearing answer set out clearly, and structured reasoning over volume of writing.

Structure and timing

130 marks in 150 minutes is a brisk ~1.15 minutes per mark, so pace matters.

Section A - Multiple choice (~20-30 marks). Target about 25-30 minutes; do scratch working for calculation items.
Section B - Short and extended response (~100-110 marks). Target about 115-120 minutes at ~1.15 min/mark.

A workable plan: ~28 minutes Section A, ~115 minutes Section B, with a final 7-8 minutes to check units, vector directions and significant figures.

Worked practice questions (exam-style)

Worked example

Question 1 (5 marks): A transformer has 200 turns on the primary coil and 50 turns on the secondary, with a primary voltage of $240\ \text{V AC}$ . (a) Calculate the secondary voltage. (b) If the transformer is ideal and the secondary current is $8.0\ \text{A}$ , calculate the primary current.

(a) For an ideal transformer the voltage ratio equals the turns ratio:

\frac{V_s}{V_p} = \frac{N_s}{N_p} \implies V_s = 240 \times \frac{50}{200} = 60\ \text{V}

(b) An ideal transformer conserves power ( $V_p I_p = V_s I_s$ ):

I_p = \frac{V_s I_s}{V_p} = \frac{60 \times 8.0}{240} = 2.0\ \text{A}

The secondary voltage is 60 V and the primary current is 2.0 A.

Worked example

Question 2 (6 marks): A satellite of mass $m$ orbits a planet of mass $M$ in a circular orbit of radius $r$ . (a) Derive an expression for the orbital period $T$ . (b) Hence state how $T^2$ depends on $r$ .

The strategy is to set gravitational force equal to centripetal force, eliminate the orbital speed in favour of the period, then rearrange for $T$ .

Step 1: Equate gravitational and centripetal forces

The gravitational force provides all of the centripetal acceleration, so:

\frac{GMm}{r^2} = \frac{mv^2}{r}.

Cancel the satellite mass $m$ from both sides and solve for $v^2$ :

v^2 = \frac{GM}{r}.

Step 2: Express $v$ in terms of the period $T$

For a circular orbit the satellite travels circumference $2\pi r$ in time $T$ , so $v = \dfrac{2\pi r}{T}$ , which gives:

v^2 = \frac{4\pi^2 r^2}{T^2}.

Step 3: Combine and solve for $T^2$

Set the two expressions for $v^2$ equal and rearrange:

\frac{4\pi^2 r^2}{T^2} = \frac{GM}{r} \implies T^2 = \frac{4\pi^2 r^3}{GM}.

Step 4: State the dependence (Kepler's third law)

Since $G$ , $M$ are constants for a given planet, $T^2 \propto r^3$ . This is Kepler's third law: the square of the orbital period is proportional to the cube of the orbital radius.

Final answer: $T = 2\pi\sqrt{\dfrac{r^3}{GM}}$ and $T^2 \propto r^3$ .

Worked example

Question 3 (6 marks): In a photoelectric experiment, a graph of maximum kinetic energy $E_k$ (in joules) versus frequency $f$ is a straight line. (a) State what the gradient and the horizontal intercept represent. (b) Explain why this graph supports the particle model of light over the wave model.

(a) The photoelectric equation is $E_k = hf - W$ , a straight line of the form $y = mx + c$ . The gradient equals Planck's constant $h$ . The horizontal intercept (where $E_k = 0$ ) is the threshold frequency $f_0 = \dfrac{W}{h}$ , and the magnitude of the vertical intercept equals the work function $W$ .

(b) The wave model predicts that brighter (higher-intensity) light would always eject electrons given enough time, and that kinetic energy should depend on intensity. Instead, $E_k$ depends linearly on frequency and there is a sharp threshold frequency below which no electrons are emitted regardless of intensity. This is explained by light arriving as discrete photons of energy $hf$ : only a photon with $hf \ge W$ can eject an electron. The frequency dependence and threshold therefore support the particle model.

Common errors students made

The 2021 VCAA examiners' report noted missing units, mixing scalar and vector quantities, treating projectile motion as one-dimensional, and confusing induced EMF with flux rather than rate of change of flux. Adding to those:

Transformer power slips - forgetting that an ideal transformer steps voltage up and current down (and vice versa), and that power is conserved.
Misreading photoelectric graphs - confusing the gradient ( $h$ ) with the work function, or the threshold frequency with the intercept value.
Frame errors in relativity - applying time dilation/length contraction with the wrong observer's measurement as the proper quantity.
Omitting comment on assumptions in extended items where the marking scheme expected it (e.g. "ideal transformer", "negligible air resistance").

How to use this paper

Sit Section A in a strict ~28-minute block, then Section B in a single ~115-minute run under exam conditions, keeping a final 7-8 minute buffer to check units, vector directions and significant figures. Mark each calculation against the official VCAA assessment report and answers at the authority page linked in the frontmatter, noting where method marks sit - stating the correct relationship earns marks even when arithmetic slips. Re-attempt any item that lost more than half its marks on a fresh page, writing the relationship and substitution on separate lines before solving. Keep an error log of recurring traps (transformer ratios, photoelectric graph features, relativistic frame choice) and re-test those item types after a week.

Use this paper well

Sit the paper under exam conditions (150 minutes, 130 marks).
Mark yourself against the official VCAA marking notes.
Compare against the Physics hub to find the syllabus dot points this paper tested.

What this paper assessed

Structure and timing

Worked practice questions (exam-style)

Common errors students made

How to use this paper

Use this paper well

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