Classification of Particles (AQA AS Physics)

Exam Questions

3 hours44 questions
1a1 mark

The strong nuclear force holds nucleons together inside the nucleus of an atom. It is mediated by exchange particles, which are constantly exchanged between the nucleons themselves.

State the name of the exchange particle for the strong nuclear force.

1b2 marks

The exchange particle of the strong nuclear force is a type of hadron.

Define the term ‘hadron’.

1c4 marks

Another type of hadron is the K+ meson, which has a strangeness +1.

       (i)         State the quark composition of a meson 

            (ii)        State the baryon number of a K+ meson 

            (iii)       Determine the quark composition of a K+ meson

1d1 mark

Describe the likely decay route between kaons and pions.

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2a5 marks

From the following set of particles

2-2-s-q--q2a-easy-aqa-a-level-physics

   identify all examples of:   

            (i) hadrons, 

            (ii)  leptons, 

            (iii)  antiparticles, 

            (iv)  charged particles, 

            (v)  exchange particles.      

 

.

2b2 marks

State the quark composition of 

      (i)   a proton, 

      (ii)   an antineutron.

2c3 marks

A sigma plus particle,∑+ , is a baryon and has a strangeness –1.

Complete the missing information in Table 1 for the ∑+.

Table 1

Number of quarks

 

Number of strange quarks

 

Baryon number

 

2d1 mark

State the name of the particle to which the sigma plus ∑ + will eventually decay. 

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3a3 marks

Name three flavours (or types) of quark.

3b2 marks

By referring to the charge on quarks, explain why the proton has a charge of +1e

3c2 marks

The discovery that the proton (and indeed, the neutron) was not a fundamental particle was a major accomplishment in particle physics.

   (i)   Explain what is meant by the term ‘fundamental particle’ 

   (ii)  Name a particle that is – to our most current knowledge – fundamental

3d2 marks

Discoveries in particle physics are usually made in very large particle accelerators, like the discovery of the Higgs Boson in the Large Hadron Collider at CERN.

Suggest two reasons why collaboration among many scientists and organisations is necessary for new discoveries in particle physics.

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4a4 marks

A baryon is a type of hadron.

Draw lines in Figure 1 below to indicate the baryon number for each particle listed.

The first has been done for you.        

2-2-s-q--q4a-easy-aqa-a-level-physics

 

4b3 marks

During  beta to the power of plus decay, a nuclear proton p turns into a neutron n, and the nucleus emits a high energy positron (a beta to the power of plus particle) and a neutrino. This process is summarised by the nuclear decay equation below:

                  p space rightwards arrow space n space plus space beta to the power of plus plus space v subscript e

By referring to the baryon number of each particle in the nuclear decay equation, explain why this decay is allowed by the laws of physics.

4c2 marks

Without reference to baryon number, identify one similarity and one difference between a proton and a neutron.

4d1 mark

Hadrons account for a large percentage of all matter in the known universe. Atoms are mostly comprised of baryons. 

State the name of another type of hadron.

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5a3 marks

Classification in physics involves grouping matter particles together according to distinct properties. The ‘Standard Model’ of physics groups particles together according to the forces they interact with, and according to conserved quantities like baryon number. 

Figure 1 shows a typical way in which matter particles in the standard model are grouped.

                              Figure 1 

2-2-s-q--q5a-easy-aqa-a-level-physics

Some of the information is missing.

Complete the missing information in the spaces provided in Figure 1.

5b2 marks

Strange particles are particles which include a strange quark, and strange quarks have a strangeness equal to –1­. 

Strangeness is a quantum number which, unlike baryon and lepton number, is not always conserved in particle interactions.

             (i)         Identify a type of particle that includes a strange quark 

             (ii)        State the interaction which does not conserve strangeness

5c4 marks

Leptons are fundamental particles. 

Table 1 shows four types of leptons: the electron , the muon μ , the electron neutrino begin mathsize 20px style v subscript e end style, and the muon neutrino v subscript mu .

 Table 1

 

Electron, e

Muon, μ

Electron neutrino, bold italic v subscript bold e

Muon neutrino, bold italic v subscript bold mu

Electron lepton number

 

 

 

 

Muon lepton number

 

 

 

 

Complete the missing information in Table 1.

  

5d1 mark

State the muon lepton number of an anti-muon neutrino, v with bar on top subscript mu.

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1a4 marks

Hadrons fall into two sub-groups.

Name each subgroup and describe the general quark structure of each. Give one example of a particle from any subgroup.

1b2 marks

Give the quark composition of an anti-proton and an anti-neutron.

1c3 marks

Determine the number of up quarks in C presubscript 24 presuperscript 55 r

1d3 marks

Determine the number of down quarks in C presubscript 24 presuperscript 55 r .

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2a3 marks

Table 1 gives information about some fundamental particles.

 Table 1

Particle

Quark structure

Charge

Strangeness

Baryon Number

 

u with bar on topu with bar on topd with bar on top

 

 

-1

sigma+ (∑+)

 

+1

 

+1

pion straight pi to the power of minus

 

-1

0

 

Complete the table by filling in the missing information. 

2b2 marks

 Cosmic ray showers are a source of high-energy pions and kaons. 

State the group of particles that pions and kaons belong to and determine the charge on a kaon with a quark structure of u with bar on top s.

2c1 mark

Kaons have a lifetime of 1.24 × 10–8 s whilst pions have a lifetime of 8.0 × 10–17 s.

Give a reason why you would expect kaons to have a longer lifetime.

2d2 marks

Another strange particle, Y , decays in the following way:

                Y rightwards arrow straight pi to the power of minus space plus p 

State what interaction produces particle and what interaction is involved in its decay.    

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3a1 mark

Write an equation representing a kaon decay.

3b3 marks

Table 1 shows three particles, two pions and one kaon.

                   Table 1

Particle

Quark combination

begin mathsize 20px style straight pi to the power of plus end style

 

K to the power of minus

 

begin mathsize 20px style straight pi to the power of 0 end style

 

 

Complete Table 1 to show the correct quark combinations.

3c4 marks

One of the lambda (logical and) baryons has a quark structure of begin mathsize 20px style u d s end style.

Determine the following properties of the lambda baryon:           

  • Charge
  • Baryon number
  • Lepton number
  • Strangeness 
3d4 marks

State the following properties of the anti-particle of the lambda baryon: 

  • Charge
  • Baryon number
  • Lepton number
  • Strangeness 

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4a1 mark

What distinguishes a lepton from other subatomic particles? 

4b4 marks

Table 1 gives information about some leptons.

 Table 1

Lepton symbol

Name

Relative Charge

Lepton Number

e to the power of plus

 

+1

 

 

muon

 

+1

v with bar on top subscript e

antielectron neutrino

 

 

 

muon neutrino

0

 

 

Complete Table 1 by filling in the missing information.

4c2 marks

A negative muon (mu to the power of minus) may decay into three leptons             2-2-s-q--q2c-medium-aqa-a-level-physics

Write down an equation representing the muon decay.

4d2 marks

Particle physics is a collaborative effort and there are have been considerable advances in this field over the past 100 years. 

 Explain why it is necessary for large teams of scientists and engineers to collaborate and validate new knowledge for these advances to occur.

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5a2 marks

What is the baryon number of an alpha (α) particle ? 

5b4 marks

Particle X has the following characteristics shown in Table 1.

 Table 1

Particle

Baryon number

Relative Charge

Lepton number

Strangeness

X

+1

+1

0

-1

 

Using Table 1, determine the quark composition of particle X and through which type of interaction it will decay.

5c2 marks

Which baryon will particle X eventually decay into? Give a reason for your answer.

5d2 marks

Explain why a baryon with quark structure u u with bar on top d cannot exist.

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1a4 marks

The ‘eightfold way’ is an organisational scheme for subatomic particles. This question uses the eightfold way to organise mesons.

 Physicists like to organise mesons in this way because certain symmetries appear if their strangeness is plotted against their electric charge.

 Figure 1 shows a plot of the eightfold way. Six particles and their quark compositions are shown at the vertices of a hexagon. The centre of the hexagon represents particles called neutral pions.

 Vertices are linked by horizontal axes, labelled S, and diagonal axes labelled q. Some additional information is missing from Figure 1.

2-2-s-q--q1a-hard-aqa-a-level-physics

Deduce the meaning of the labels S and q in Figure 1 and explain your reasoning for both.

1b4 marks

Use Figure 1 to determine the quark composition of the K to the power of plus, straight pi to the power of plus, K with bar on top to the power of space 0 end exponent and K to the power of minus

1c2 marks

Deduce a possible quark composition for a neutral pion and explain your reasoning.

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2a4 marks

The baryon decuplet is a vision tool used by particle physicists to classify groups of particles called baryons.

Discuss the properties of baryons.

2b3 marks

In the baryon decuplet, strangeness S is plotted on the horizontal axes and charge Q is plotted on the diagonal axes, as shown in Figure 1. Some information is missing.

                              Figure 1

qu2a-fig-1

Deduce the quark composition of the Ω baryon, using each axis to justify your answer.

2c4 marks

Deduce the quark composition and an appropriate symbol for the missing baryon in Figure 1.

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3a3 marks

The discovery of the Higgs Boson marked a huge accomplishment for particle physicists. 

The Higgs Boson was hypothesised by Peter Higgs and his team in 1964 as a mechanism to explain why some particles have mass. It was discovered by a large collaborative effort at the CERN particle physics laboratory in 2012. 

Explain what is meant by the term ‘hypothesised’ and suggest why it took over forty years to discover the Higgs Boson.

3b3 marks

The experimental results which hinted at the existence of a new particle caught the attention of media worldwide.

 While public excitement grew, the scientists involved in the experiment were cautious before confirming that the results proved the existence of a new particle. In fact, confirmation came many months after the first set of results were reported.

Discuss why it takes many months after results are first discovered to confirm the existence of a new particle.

3c4 marks

Other exciting results from experiments in particle physics have contributed to the field’s considerable advances over the past 100 years.

 State and explain two reasons which demonstrate why collaboration between scientists and engineers is necessary in order for such advances to be made.

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4a3 marks

A young student of physics reads up about particles and anti-particles.

In their physics lesson, they excitedly tell their teacher how they learned that a proton has an anti-particle called an anti-proton, and the neutron has an anti-particle called an anti-neutron.

They go on to say that, since the neutron is neutrally charged, it is its own anti-particle.

Identify the student’s misconception and explain why they are incorrect.

4b2 marks

Suggest another particle which is an example of being its own anti-particle and explain your reasoning.

4c3 marks

Interactions between protons and neutrons can temporarily violate conservation laws.

 One such interaction is shown in Figure 1:

2-2-s-q--q4c-hard-aqa-a-level-physics

(i)         Identify the type of interaction shown in Figure 1. 

(ii)        By referencing the properties of the exchange particle, explain how it temporarily violates conservation laws.

4d4 marks

The extent to which conservation laws can be violated is governed by Heisenberg’s Uncertainty Principle.

 Simply put, this principle says that the uncertainty in some quantity of energy ΔE multiplied by the uncertainty in a time interval Δt must always be constant. This can be written as:

              ΔE × Δt  = fraction numerator h over denominator 4 straight pi end fraction

The range of the strong force is around 1 × 10–15 m. 

 Assuming the strong force is mediated at near the speed of light, show that pions are about 200 times more massive than electrons.

You may use the energy-mass equation: 

               E = mc2

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