AQA AS Level Physics Paper 1, June 2022: Question 1

6 marks · Medium difficulty · Short Answer

Complete particle properties (baryon number, charge, strangeness) for a strong interaction producing a sigma-plus and particle Y, identify a particle from its quark structure, and deduce which particle has the greater charge-to-mass ratio with justification.

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Question

Question text

01 A sigma-plus (Σ+) particle and an unidentified particle Y are produced by the strong

interaction between a positive pion (π+) and a proton (p).

This interaction is represented by the equation:

π+ + p → Σ+ + Y

01.1 Complete Table 1 to show the baryon number B, charge Q and strangeness S for the

particles in this interaction.

[2 marks]

Table 1

π+ p Σ+ Y

B 0

Q +1 +1 +1

S +1

01.2 Which particle in Table 1 has the quark structure uus?

Tick ( ) one box.

[1 mark]

π+

Σ+

Y 3

01.3 Deduce which particle, π+ or Y, has the greater charge-to-mass ratio.

Justify your conclusion.

[3 marks]

Mark scheme

Show the mark scheme

Question Answers Additional Comments/Guidance Mark AO

01.1 2 rows correct 2 1 x AO1

+ + 1 x AO2

3 rows correct π p Σ Y

B 0 (+)1 (+)1 0

Q +1 +1 +1 (+)1

S 0 0 −1 +1

01.2 Tick 3rd box only - Σ+ 1 AO2

01.3 Y has a greater rest energy than 𝜋𝜋+ / Y has a greater mass Treat Y is larger than the 𝜋𝜋+as neutral. 3 3 x AO3

than 𝜋𝜋+

MP1: Condone error in mass comparisons

where Y is identified as having a greater rest

6 energy.

𝜋𝜋+

and Y have the same charge / or charge on both particles

𝜋𝜋+ and 𝐾𝐾+ 𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 Both have a charge of +1(e)

identified as having charge of (+)1 /

Accept for mp2:

Y is a kaon / Y is a k meson Y contains an s or 𝑠𝑠̅ quark which is more

massive than u or d quarks in the pion / Y

contains an s or 𝑠𝑠̅ quark whereas pion does

not.

𝜋𝜋+ is 1st generation (meson) while Y is 2nd

generation (meson)

Loses MP2 for stating incorrect number of

quarks for Y or stating that Y is a baryon.

Accept converse statement

𝜋𝜋+has a greater charge-to-mass ratio because it has the

Error carried forward for charge on Y from 01.1

same charge as Y and less mass than Y / Y will have a greater specific charge where Y

𝜋𝜋+ has a greater specific charge

has charge greater than +4

Total 6

How to answer it

Particle Interactions, Conservation Laws and Specific Charge

AQA AS Level Physics • Particles Topic

What this question tests

This question assesses your understanding of particle interactions, conservation laws (baryon number, charge, and strangeness), quark compositions of hadrons, and the ability to compare specific charge (charge-to-mass ratios) between subatomic particles using rest energy or mass arguments.

Part 01.1: Completing Particle Conservation Tables

Question: Complete Table 1 to show baryon number (B), charge (Q), and strangeness (S) for the interaction equation pi⁺ + p → Σ⁺ + Y.

✅ Correct Table Values

π⁺: B = 0, Q = +1, S = 0
p: B = 1, Q = +1, S = 0
Σ⁺: B = 1, Q = +1, S = -1
Y: B = 0, Q = +1, S = +1

💡 Key Knowledge

Baryon number (B): Quarks have B = +1/3, antiquarks have B = -1/3. Mesons have B = 0; baryons have B = 1.
Strangeness (S): Conserved in strong interactions. The Kaon (Y) carrying S = +1 balances out the S = -1 of the Σ⁺ particle.

🧠 Exam Technique

Always verify your completed rows across the equation using conservation laws before writing down the final numbers. For a strong interaction, B, Q, and S must all balance on both sides of the arrow.

❌ Common Errors

Students often mistake the baryon number of mesons (like the unidentified particle Y, which is a K⁺ meson) as 1 instead of 0, or miscalculate strangeness signs.

🎯 Mark Allocation: 2 marks total. 2 rows correct = 1 mark; 3 rows correct = 2 marks.

Part 01.2: Identifying Quark Structure

Question: Which particle in Table 1 has the quark structure uus?

✅ Correct Answer

Tick the 3rd box only: Σ⁺

💡 Key Knowledge

A Sigma-plus (Σ⁺) is a baryon containing strangeness S = -1. Its quark composition is uus . Let's check the charges: u = +2/3, u = +2/3, s = -1/3. Total charge = (+2/3) + (+2/3) + (-1/3) = +1, which matches Q for Σ⁺.

🧠 Exam Technique

Remember that strange quarks carry a charge of -1/3 and a strangeness of -1. Use fractional charge arithmetic to quickly verify baryon quark structures in multiple-choice or tick-box questions.

🎯 Mark Allocation: 1 mark for ticking the 3rd box (Σ⁺) exclusively.

Part 01.3: Charge-to-Mass Ratio Deduction

Question: Deduce which particle, pi⁺ or Y, has the greater charge-to-mass ratio. Justify your conclusion.

✅ Correct Answer

π⁺ has the greater charge-to-mass ratio (or specific charge).

📐 Step-by-Step Justification

Compare Charge: Both the pion (π⁺) and particle Y (the K⁺ kaon) have the exact same charge of +1e .
Compare Mass / Rest Energy: Particle Y contains a strange quark/antiquark (which is more massive than the up/down quarks found in a pion). Therefore, Y has a greater rest energy / mass than π⁺.
Conclusion: Since specific charge is defined as charge ÷ mass , the particle with the smaller mass (π⁺) while sharing the same charge must have the greater charge-to-mass ratio.

🧠 Exam Technique

Always state the formula or relationship clearly: specific charge = charge / mass. Explicitly point out what is equal (charge) and what differs (mass) to secure all marking points seamlessly.

❌ Common Errors

Failing to explicitly link the lighter mass of the pion to a larger ratio, or confusing the quark makeup leading to incorrect mass assumptions about kaons versus pions.

🎯 Mark Allocation: 3 marks.
• MP1: States Y has greater mass / rest energy (or converse for π⁺).
• MP2: States both particles have the same charge (+1).
• MP3: Concludes logically that π⁺ has the greater charge-to-mass ratio due to having a smaller mass for the same charge.

Topics

Physics · 3.2 Particles and radiation

Question and mark scheme from the AQA AS Level Physics examination, Paper 1, June 2022. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.