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NESA Physics Deep inside the Atom

15 sample questions with marking guides and sample answers · Avg. score: 76%

Q33

2025

NESA

6 marks

Q33

6 marks

Analyse the role of experimental evidence and theoretical ideas in developing the Standard Model of matter.

Reveal Answer

Experiments and theoretical ideas have both been critical in the development of the Standard Model of matter.

Particle accelerators have been used to verify key ideas about fundamental particles and the structure of matter. Particle accelerators allow for small wavelength 'matter probes' at high energies, giving high resolution for probing the structure of matter.

Examples of particle accelerator use in the development of the Standard Model include:

Verification of the electroweak theory, which says that the electromagnetic and weak nuclear forces are a result of the same interaction.
The discovery of a Higgs Boson, many decades after it was first proposed as necessary in explaining the mass of particles.
Verification of the existence of quarks by showing the protons and neutrons have internal structure.

Earlier experiments used simpler equipment such as the cloud chamber which was used to discover antimatter following its earlier theoretical prediction.

Many experiments have verified earlier theoretical ideas, and these confirmations have then in turn allowed the proposal of further ideas, which have in turn later been verified by experiments.

Marking Criteria

Descriptor	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 how experimental evidence and theoretical ideas contributed to the development of the Standard Model of matter	5
Describes experiment(s) and idea(s) relating to fundamental particles and/or forces AND links these to the Standard Model of matter	4
The student response meets all criteria of the 2-mark band, and additionally meets the majority of criteria in the 4-mark band.	3
Outlines experiments and/or ideas relating to fundamental particles or forces	2
Provides some relevant information	1
None of the above	0

Q12

2023

QCAA

Paper 1

1 mark

Q12

1 mark

What is a consequence of symmetry in particle interactions?

The law of conservation of momentum is obeyed.

Charges on particles will always be different.

Antiparticles travel backwards through time.

Total mass of the particles will decrease.

Reveal Answer

The law of conservation of momentum is obeyed.

Correct Answer

According to Noether's theorem, continuous symmetries in physical systems correspond to conservation laws; specifically, invariance under spatial translation leads directly to the conservation of momentum.

Charges on particles will always be different.

While gauge symmetry leads to the conservation of electric charge, it does not dictate that interacting particles must possess different charges.

Antiparticles travel backwards through time.

While the Feynman-Stueckelberg interpretation of CPT symmetry mathematically treats antiparticles as moving backward in time, this is a representational tool rather than the fundamental physical consequence of symmetry, which is conservation.

Total mass of the particles will decrease.

Symmetry leads to the conservation of quantities (like total mass-energy via time translation symmetry), not a mandatory decrease in mass.

Q33

2023

NESA

9 marks

Q33

9 marks

Consider the following statement.

"The interaction of subatomic particles with fields, as well as with other types of particles and matter, has increased our understanding of processes that occur in the physical world and of the properties of the subatomic particles themselves."

Justify this statement with reference to observations that have been made and experiments that scientists have carried out.

Reveal Answer

Marking Criteria

Descriptor	Marks
Provides a reasoned detailed justification for the statement with explanation referencing at least TWO observations and at least TWO experiments	9
Provides a justification for the statement with explanation referencing at least TWO observations and at least TWO experiments	8
The student response meets all criteria of the 6-mark band, and additionally meets the majority of criteria in the 8-mark band.	7
Provides a justification for the statement with an explanation of an observation/experiment of particle–field interactions and an observation/experiment of particle–particle interactions	6
The student response meets all criteria of the 4-mark band, and additionally meets the majority of criteria in the 6-mark band.	5
Provides details of TWO experiments or observations and how they relate to the statement	4
The student response meets all criteria of the 2-mark band, and additionally meets the majority of criteria in the 4-mark band.	3
Relates the statement to an experiment or observation OR Describes relevant experiments or observations	2
Provides some relevant information	1
None of the above	0

Q20

2022

QCAA

Paper 1

1 mark

Q20

1 mark

Which option lists the gauge bosons in ascending order of the strength of force they mediate?

W boson < Z boson < Photon

Gluon < Z boson < W boson

Photon < W boson < Gluon

Z boson < Photon < Gluon

Reveal Answer

W boson < Z boson < Photon

This option compares two mediators of the weak force (W and Z bosons) against the photon; however, the correct hierarchy of fundamental forces places the strong force (mediated by gluons) as the strongest, which is better represented in other options.

Gluon < Z boson < W boson

Gluons mediate the strong nuclear force, which is the strongest of the fundamental forces, so they should appear last in an ascending list, not first.

Photon < W boson < Gluon

The electromagnetic force (mediated by photons) is stronger than the weak nuclear force (mediated by W bosons), so the photon should be listed after the W boson in an ascending order.

Z boson < Photon < Gluon

Correct Answer

This correctly lists the mediators in ascending order of force strength: the Z boson mediates the weak nuclear force (weakest here), the photon mediates the electromagnetic force, and the gluon mediates the strong nuclear force (strongest).

Q22

2023

QCAA

Paper 1

3 marks

Q22

3 marks

Particles move at a rate of $1.3\times10^6$ times per second around a circular particle accelerator with a radius of 35 m.

Calculate the average speed of the particles. Show your working.

Average speed = ______ $ms^{-1}$ (two significant figures)

Reveal Answer

$C = 2\pi r = 2 \times \pi \times 35 \approx 219.91 \text{ m}$

$f = \frac{1}{T}$

$\therefore v = \frac{2\pi r}{T} = 219.91 \times 1.3 \times 10^6 = 2.86 \times 10^8 \text{ m s}^{-1}$

Average speed $= 2.9 \times 10^8 \text{ m s}^{-1}$ (to two significant figures)

Marking Criteria

Descriptor	Marks
Recognises the scenario relates to average speed of objects in uniform circular motion	1
Provides appropriate mathematical reasoning	1
Calculates the average speed of the particles	1

2022

QCAA

Paper 2

2 marks

Contrast the properties of up quarks and tau particles.

Reveal Answer

Up quarks are fundamental particles that experience the strong nuclear force and may be combined with other quarks to form mesons and baryons.

Tau particles are also fundamental particles belonging to the lepton group of subatomic particles. These particles experience the weak nuclear force, and unlike quarks they do not combine with other leptons to form other subatomic particles.

Marking Criteria

Descriptor	Marks
Identifies a difference between the nature of particles	1
Identifies a difference between interaction forces	1

Q15

2024

VCAA

1 mark

Q15

1 mark

At the Australian Synchrotron, electrons are accelerated to close to the speed of light, $c$ , by the linear accelerator.

Consider electrons that enter the Australian Synchrotron booster ring with a Lorentz factor $\gamma = 200$ , and as a result of further acceleration in that ring reach a much higher value, with a Lorentz factor $\gamma = 2000$ .

Which one of the following best describes the effect of the booster ring on each electron's speed and energy?

The electron's speed increases by a large amount and its energy increases by a large amount.

The electron's speed increases by a small amount and its energy increases by a large amount.

The electron's speed increases by a large amount and its energy increases by a small amount.

The electron's speed increases by a small amount and its energy increases by a small amount.

Reveal Answer

The electron's speed increases by a large amount and its energy increases by a large amount.

Incorrect. Since the electron is already traveling close to the speed of light when $\gamma = 200$ , its speed can only increase by a very small fraction to approach $c$ .

The electron's speed increases by a small amount and its energy increases by a large amount.

Correct Answer

Correct. The electron's speed is already very close to $c$ , so it only increases by a small amount, but its total energy, given by $E = \gamma mc^2$ , increases by a factor of 10, which is a large amount.

The electron's speed increases by a large amount and its energy increases by a small amount.

Incorrect. The speed only increases by a small amount because it cannot exceed the speed of light, while the energy increases by a large amount.

The electron's speed increases by a small amount and its energy increases by a small amount.

Incorrect. The energy increases by a large amount because it is directly proportional to the Lorentz factor ( $E = \gamma mc^2$ ), which increases tenfold from 200 to 2000.

Q12

2025

SCSA

5 marks

Q12

Scientists have discovered a new particle they call a 'pentaquark'. It consists of two up quarks, two down quarks and an anti-strange quark. They determined its mass to be $1.54\text{ GeV}/c^2$ .

Q12a

2 marks

Determine the overall charge of a pentaquark.

Reveal Answer

Charges on the quarks are : $2 \times \frac{2}{3}$ , $2 \times \frac{-1}{3}$ , $\frac{1}{3}$

Overall charge is $+1$

Marking Criteria

Descriptor	Marks
Correctly identifies charges on all quarks: $2 \times \frac{2}{3}$ , $2 \times \frac{-1}{3}$ , $\frac{1}{3}$	1
Adds to correct total: $+1$	1

Q12b

3 marks

Calculate the mass of a pentaquark in kilograms.

Reveal Answer

$m = \frac{E}{c^2} = \frac{(1.54 \times 10^9)(1.60 \times 10^{-19})}{(3.00 \times 10^8)^2} = 2.74 \times 10^{-27} \text{ kg}$

Marking Criteria

Descriptor	Marks
Uses $E = mc^2$ rearranged for $m$ : $m = \frac{E}{c^2}$	1
Substitutes values and converts GeV to Joules: $m = \frac{(1.54 \times 10^9)(1.60 \times 10^{-19})}{(3.00 \times 10^8)^2}$	1
Calculates answer: $m = 2.74 \times 10^{-27} \text{ kg}$	1

Q10

2020

QCAA

Paper 1

1 mark

Q10

1 mark

The force that quarks experience that leptons do not is the

weak force.

strong force.

normal force.

electromagnetic force.

Reveal Answer

weak force.

Both quarks and leptons experience the weak nuclear force, which is responsible for processes such as beta decay.

strong force.

Correct Answer

Quarks carry color charge and interact via the strong nuclear force, whereas leptons do not carry color charge and are completely unaffected by this force.

normal force.

The normal force is a macroscopic contact force arising from electromagnetic interactions between atoms, not a fundamental force distinguishing subatomic particles.

electromagnetic force.

Both quarks and charged leptons (such as electrons) possess electric charge and therefore experience the electromagnetic force.

2021

QCAA

Paper 1

1 mark

Leptons do not experience the

weak force.

strong force.

gravitational force.

electromagnetic force.

Reveal Answer

weak force.

All leptons participate in the weak nuclear interaction, which is responsible for processes such as beta decay.

strong force.

Correct Answer

Leptons do not carry color charge and therefore do not interact via the strong nuclear force; this is the primary distinction between leptons and quarks.

gravitational force.

Gravity acts on all particles that possess mass or energy, so leptons do experience the gravitational force.

electromagnetic force.

Charged leptons (like electrons, muons, and taus) experience the electromagnetic force, although neutral leptons (neutrinos) do not.

2023

QCAA

Paper 1

1 mark

Photons are

gauge bosons that exhibit wave characteristics.

particles that can only travel in a medium.

mediators of the weak nuclear force.

leptons with no charge.

Reveal Answer

gauge bosons that exhibit wave characteristics.

Correct Answer

Photons are the gauge bosons responsible for the electromagnetic force and exhibit wave-particle duality, displaying properties of both waves and particles.

particles that can only travel in a medium.

Unlike mechanical waves (like sound), photons are electromagnetic radiation and can travel through a vacuum without requiring a physical medium.

mediators of the weak nuclear force.

Photons mediate the electromagnetic force, whereas the weak nuclear force is mediated by $W$ and $Z$ bosons.

leptons with no charge.

Photons are bosons, not leptons; leptons are a different family of particles that includes electrons and neutrinos.

Q20

2025

NESA

1 mark

Q20

1 mark

Consider the possibility of an electron and a positron colliding in a particle accelerator to produce a proton and an antiproton, as shown in the equation below.

electron + positron $\rightarrow$ proton + antiproton

Which statement makes the correct conclusion about the possibility of such a reaction, and provides a plausible reason for this conclusion?

The reaction is impossible because electrons and positrons will combine to produce a single neutral particle.

The reaction is possible because the masses of the proton and antiproton are the result of their relativistic velocities.

The reaction is possible because the masses of the proton and antiproton come mainly from energy supplied by the accelerator.

The reaction is impossible because protons are much more massive than electrons and hence the reaction violates the law of conservation of mass.

Reveal Answer

The reaction is impossible because electrons and positrons will combine to produce a single neutral particle.

An electron and positron typically annihilate to produce at least two photons in order to conserve momentum, rather than combining into a single neutral particle.

The reaction is possible because the masses of the proton and antiproton are the result of their relativistic velocities.

The mass of a proton or antiproton is an intrinsic property (rest mass) and is not caused by relativistic velocities.

The reaction is possible because the masses of the proton and antiproton come mainly from energy supplied by the accelerator.

Correct Answer

In a particle accelerator, the high kinetic energy of the colliding electron and positron can be converted into the much larger rest masses of a proton and antiproton, following the mass-energy equivalence principle ( $E=mc^2$ ).

The reaction is impossible because protons are much more massive than electrons and hence the reaction violates the law of conservation of mass.

While protons are indeed much more massive than electrons, the law of conservation of mass-energy applies, not just rest mass. The additional mass is created from the kinetic energy supplied by the accelerator.

2020

QCAA

Paper 1

1 mark

Select the list containing the six types of quarks.

in, out, up, down, top and bottom

right, left, charm, strange, in and out

up, down, charm, strange, top and bottom

charm, strange, right, left, top and bottom

Reveal Answer

in, out, up, down, top and bottom

This list is incorrect because "in" and "out" are not types of quarks. The correct flavors missing from this list are charm and strange.

right, left, charm, strange, in and out

This list is incorrect because "right", "left", "in", and "out" are not quark flavors. Right and left typically refer to chirality or direction, not particle type.

up, down, charm, strange, top and bottom

Correct Answer

This is the correct list. According to the Standard Model of particle physics, the six quark flavors are up, down, charm, strange, top, and bottom.

charm, strange, right, left, top and bottom

This list is incorrect because "right" and "left" are not quark flavors. The list is missing the up and down quarks.

2021

QCAA

Paper 2

1 mark

List the four gauge bosons in the Standard Model.

Reveal Answer

Gluon
Photon
W boson
Z boson

Marking Criteria

Descriptor	Marks
Lists the four gauge bosons	1

2024

NESA

1 mark

Which of the following is a fundamental particle in the Standard Model of matter?

Hadron

Neutron

Photon

Proton

Reveal Answer

Hadron

Incorrect. Hadrons are composite particles made of two or more quarks held together by the strong force, meaning they are not fundamental.

Neutron

Incorrect. A neutron is a composite particle made of three quarks (one up and two down), so it is not a fundamental particle.

Photon

Correct Answer

Correct. The photon is an elementary particle in the Standard Model, specifically a gauge boson that mediates the electromagnetic force.

Proton

Incorrect. A proton is a composite particle made of three quarks (two up and one down), meaning it can be broken down further and is not fundamental.

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