How many NESA Physics questions cover Light and Special Relativity?

AusGrader has 68 NESA Physics questions on Light and Special Relativity, all with instant AI grading and detailed marking feedback.

NESA (HSC) Physics — Light and Special Relativity Questions & Answers | AusGrader

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?

A

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

B

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

C

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

D

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

Q19

2025

NESA

1 mark

Q19

1 mark

A system consists of a sealed glass jar containing some oxygen and a small strip of magnesium.

The magnesium reacts with the oxygen to produce magnesium oxide as a product. Energy is released from the system in this reaction.

The mass of the system will

A

increase because oxygen is added to the magnesium.

B

decrease because energy is removed from the system.

C

increase because energy is added to the system by the reaction.

D

decrease because magnesium and oxygen are lost in the reaction.

Q26

2024

NESA

3 marks

Q26

3 marks

Muons are unstable particles produced when cosmic rays strike atoms high in the atmosphere. The muons travel downward, perpendicular to Earth's surface, at almost the speed of light.

Classical physics predicts that these muons will decay before they have time to reach Earth's surface.

Explain qualitatively why these muons can reach Earth's surface, regardless of whether their motion is considered from either the muon's frame of reference or the Earth's frame of reference.

In the muon's reference frame, the distance travelled is less than that observed by a stationery observer on Earth's surface, due the effects of length contraction. This shortened distance means that they will get further than would be expected by an observer observing the rest length.

From the Earth's frame of reference, the time dilation means that the half-life of the muon is dilated compared to the half-life measured in the rest frame of the muon. This greater time allows more muons to reach the ground than would otherwise be expected.

Marking Criteria

Descriptor	Marks
Explains why muons reach the Earth's surface with reference to relativistic effects in both frames of reference	3
Outlines some relativistic effects that apply to the muon OR Explains one relativistic effect that applies to the muon	2
Provides some relevant information	1
None of the above	0

Q32

2025

NESA

8 marks

Q32

8 marks

Analyse the consequences of the theory of special relativity in relation to length, time and motion. Support your answer with reference to experimental evidence.

The two postulates of special relativity are: the speed of light in a vacuum is an absolute constant, and all inertial frames of reference are equivalent.

The consequences of these postulates are time dilation, length contraction and relativistic momentum dilation. Time dilation means that the measured time between events increases as the speed of an observer increases. Length contraction means that the length of an object decreases as the speed of an observer increases, and relativistic momentum dilation means that objects (with mass) cannot travel at c as it takes increasing amounts of energy to accelerate objects as they approach the speed of light.

Length contraction and time dilation can both be seen in observations of muons at Earth's surface. The short half-life of muons suggests that there should be very few of them that arrive at Earth's surface from their point of origin high in Earth's atmosphere, but the muon flux is greater than suggested by half-life and distance travelled alone. However, when the distance travelled is considered from the muon's frame of reference, it is length-contracted according to $l = l_0 \sqrt{\left(1 - \frac{v^2}{c^2}\right)}$ , giving an effective shorter distance for them to travel. From the perspective of an observer on Earth's surface, the time taken for them to decay is dilated, giving an effective greater amount of time for them to travel before decaying.

The effects of relativistic momentum can be seen in particle accelerators in terms of the increasing amounts of energy to required to accelerate the particles as they approach the speed of light – it is though the objects are much more massive than they are.

Marking Criteria

Descriptor	Marks
Provides a comprehensive analysis of the consequences of special relativity on time, length and motion Refers to applicable experimental evidence	8
Provides a thorough analysis of the consequences of special relativity on time, length and motion Refers to applicable experimental evidence	7
The student response meets all criteria of the 5-mark band, and additionally meets the majority of criteria in the 7-mark band.	6
Provides analysis of the consequences of special relativity on time and/or length and/or motion Refers to some relevant experimental evidence	5
The student response meets all criteria of the 3-mark band, and additionally meets the majority of criteria in the 5-mark band.	4
Makes some reference to special relativity and/or related experimental evidence	3
The student response meets all criteria of the 1-mark band, and additionally meets the majority of criteria in the 3-mark band.	2
Provides some relevant information	1
None of the above	0

Q22

2023

NESA

3 marks

Q22

3 marks

A spacecraft passes Earth at a speed of $0.9c$ . The spacecraft emits a light pulse every $3.1 \times 10^{-9}\ \text{s}$ , as measured by the crew on the spacecraft.

What is the time between the pulses, as measured by an observer on Earth?

\begin{align*} t_v &= \frac{t_0}{\sqrt{1 - \frac{v^2}{c^2}}}\\ &= \frac{3.1 \times 10^{-9}}{\sqrt{1 - 0.9^2}}\\ &= 7.1 \times 10^{-9} \text{ s} \end{align*}

Marking Criteria

Descriptor	Marks
Calculates the time between the pulses, relative to an observer on Earth	3
Provides some correct steps in calculating the time between the pulses, relative to an observer on Earth	2
Provides some relevant information	1
None of the above	0

NESA Physics Light and Special Relativity

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