Conservation Laws & Particle Interactions (AQA AS Physics)

Exam Questions

3 hours43 questions
1a3 marks

The following equation for beta to the power of minusdecay of Uranium – 235 (U presubscript 92 presuperscript 235) into an isotope of Neptunium (Np).

2-3-s-q--q1a-easy-aqa-a-level-physics

Complete the missing values in the beta to the power of minus decay equation.

1b4 marks

Table 1 shows the two of the four fundamental interactions and their corresponding exchange particles.

 Table 1

Fundamental Interaction

Exchange particle

 

Photon

Weak Nuclear Force

 

   (i)   Complete the table by filling in the missing information in each column 

   (ii)   State two more fundamental interactions

1c1 mark

State the property that all particles must possess if they experience the electromagnetic interaction.

1d2 marks

Figure 1 shows a Feynman diagram for an electromagnetic interaction between two electrons.

2-3-s-q--q1d-easy-aqa-a-level-physics

There is a space provided in Figure 1 is where the exchange particle for this interaction is missing. 

(i)
Identify the symbol of the exchange particle for this interaction in the space provided on Figure 1  

(ii)     Describe what the Feynman diagram is showing

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2a3 marks

The equation below represents a theoretical interaction of a kaon with a proton, which might result in the production of a pion and a neutron: 

               K to the power of 0 plus p space rightwards arrow space n space plus space straight pi to the power of plus

Complete the information in Table 1 for the collision:

 Table 1

Quantum number

Total before collision

Total after collision

Charge

 

 

Baryon

 

 

Lepton

 

 

2b2 marks

Hence, or otherwise, explain if this theoretical interaction is permitted by the laws of physics. 

2c1 mark

The neutron resulting from this interaction will eventually decay.

The following equation represents the decay of a neutron:

               n space rightwards arrow space p space plus space e to the power of minus space plus space v with bar on top subscript e

Complete the equation below which shows the decay of the neutron in terms of its internal quark change only:

                  ——rightwards arrow space u space plus e to the power of minus plus v with bar on top subscript e

2d1 mark

State the name of the fundamental interaction responsible for the decay of a neutron into a proton.

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3a5 marks

The four fundamental interactions of the universe govern the interactions and behaviour of all matter. 

The interactions vary in strength from weakest to strongest.

Identify and arrange all four fundamental interactions in order of their strength, in the spaces provided in Figure 1:

2-3-s-q--q3a-easy-aqa-a-level-physics

3b2 marks

The four fundamental interactions are able to transmit their influence across a range of distances, from very small scales on the order of 10–15 m to infinite distances across the universe. 

 State the two fundamental interactions that have an infinite range.

3c2 marks

Explain why electrons do not interact with the strong nuclear interaction.

3d3 marks

Figure 2 shows an interaction between a nuclear proton and an electron.

2-3-s-q--q3d-easy-aqa-a-level-physics

(i)       State the name of the interaction shown in Figure 2 

(ii)
 Identify the symbol for the exchange particle of the interaction shown in Figure 2 in the space provided   

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4a3 marks

Conservation laws are useful to determine whether certain particle interactions are allowed by the laws of physics.

Physicists can predict unseen interactions using conservation laws, which experimentalists then look for in large particle accelerators.

One such interaction between a delta particle Δ0 and a kaon K0 is predicted below:

                   begin mathsize 22px style increment to the power of 0 space plus space K to the power of 0 space rightwards arrow space K to the power of plus space end exponent plus space end style+            

Using the law of conservation of charge, state and explain whether the interaction is expected to be found by experimentalists.

4b2 marks

State two additional quantities that must be conserved in all particle interactions.

4c1 mark

Strange quarks interact with the electromagnetic, strong and weak nuclear forces.

 ‘Strangeness’ is a type of quantity which is associated with strange quarks. Physicists can measure strangeness to investigate all particle interactions involving strange quarks.

Which fundamental interaction does not conserve strangeness?

4d1 mark

In the vacuum of space, a principle of quantum physics says that particle-antiparticle pairs can be created ‘out of nothing’.

This is allowed by the laws of physics only if the particle-antiparticle pair annihilate very quickly after being created.

In the list given below, circle the conservation law which is violated by spontaneous creation of a particle-antiparticle pair in a vacuum. 

Conservation of momentum

Conservation of energy

Conservation of charge

Conservation of lepton number

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5a4 marks

(i)      State the property of all particles that interact with gravity 

(ii)
Hence, or otherwise, circle all particles that interact with gravity in the list given below                      

Virtual photon

Proton

Muon

Up quark

Positron

5b3 marks

In 1964, physicists observed the following interaction for the first time:

          K to the power of minus space plus space p space rightwards arrow space K to the power of 0 space plus space K to the power of plus space plus space X

Use the law of conservation of charge to deduce the charge of particle X.

5c3 marks

State and explain whether particle X in part (b) is a lepton.

5d1 mark

The interaction described in part (b) is a strong interaction. 

State the type of particles which are subject to the strong interaction.

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1a3 marks

Explain what is meant by an exchange particle and name the exchange particle that mediates the electromagnetic force.   

1b3 marks

For the following decay to be possible each of the baryon number, lepton number and charge must be conserved.

            n space plus space mu to the power of plus space rightwards arrow space p space plus space stack v subscript u with bar on top

Use these rules to show that the following decay is possible.

1c2 marks

Below are examples of two particle decays: 

   Decay 1:       space pplus space straight pi to the power of minus space rightwards arrow space straight K to the power of minus space plus space straight pi to the power of plus               

   Decay 2: begin mathsize 20px style p end styleplus space stack v subscript e with bar on top space rightwards arrow space n space plus space e to the power of plus                 

State, with a reason, which of these decays is not possible.

1d3 marks

The decay equation

              begin mathsize 20px style p end styleplus space pi to the power of minus space rightwards arrow spacebegin mathsize 20px style n end styleplus space K to the power of minus space plus space straight pi to the power of plus

Determine which conservation law is violated within this decay. Show your working clearly. Explain why this decay is still possible despite this violation.

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2a2 marks

During beta to the power of minus decay of a nucleus, both the nucleon composition and the quark composition change. 

Deduce the change in quark composition and the type of interaction that occurs in this decay. 

2b4 marks

Write the beta to the power of minus decay equation on a quark level.

2c3 marks

For beta to the power of minus decay to be possible each of baryon number, lepton number and charge must be conserved. 

Use these rules to show that the decay in part (b) is possible.

2d2 marks

State two more conservation laws that are obeyed in all nuclear interactions.

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3a2 marks

Define what is meant by the term fundamental particle in physics and give one example of a fundamental particle.

3b4 marks

A physicist is attempting to analyse an electron capture event of a proton. 

Write down the equation that represents this interaction. 

The proton numbers, nucleon numbers and appropriate symbols of all the particles should be shown.

3c4 marks

Show in terms of any three conservation laws, that this interaction is permitted.

3d2 marks

State the strangeness of an electron and explain why it has this value.

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4a2 marks

In alpha decay, only one particle is emitted. 

Explain how baryon number and charge are conserved in alpha decay.

4b3 marks

Particle X decays in the following way: 

               X space rightwards arrow space straight pi to the power of plus space end exponent plus space straight pi to the power of 0

Deduce the relative charge, baryon number and lepton number of particle X.

4c2 marks

Deduce whether X is a meson, baryon or lepton, explaining how you arrive at your answer. 

4d3 marks

Particle X is a strange particle. 

Determine the quark combination of particle X. Hence or otherwise, state its name. Clearly show your working.

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5a5 marks

A proposed particle interaction is:

                  begin mathsize 20px style p end styleplus space e to the power of plus space rightwards arrow space e to the power of minus space plus spaceΣ0  + K+      

 Σ0 has a quark structure of begin mathsize 20px style u d s end style.

Use the principles of conservation of charge, baryon number, lepton number and strangeness to determine whether this decay is possible.

5b3 marks

Σ0  is part of a family of baryons called Sigma baryons. They are all strange particles. 

Determine the quark combination of the Σ+ baryon. Clearly show your working.

5c4 marks

Determine the charge, baryon number, lepton number and strangeness of a particle with the quark combination d d s. 

Clearly explain your reasoning for each.

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1a3 marks

Electron capture is one of the ways a nucleus attains stability. 

In this process, a proton in the nucleus ‘captures’ an inner-shell electron. While the mass number is unchanged, the atomic number decreases by 1, and a highly energetic particle is released.

Deduce the type of interaction responsible for this process and explain your reasoning.

1b4 marks

By writing an appropriate equation for this process and applying the laws of particle physics, identify the highly energetic particle emitted in this process. 

1c5 marks

At the quark level, only some are directly involved in this process. Those which are not are sometimes called ‘spectator quarks’. 

(i)       Use your equation to sketch a suitable Feynman diagram for this process. 

(ii)
Sketch another Feynman diagram in terms of the quarks directly involved in electron capture. Do not include spectator quarks.      
1d2 marks

A similar process known as muon capture is being investigated for use in the disposal of highly radioactive waste.A highly energetic muon beam causes muons to be captured by protons in the nuclei of the radioactive isotopes in order to convert them into more stable isotopes.

Predict the equation and sketch a Feynman diagram for this process.

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2a2 marks

The virtual photon mediates the electromagnetic force. 

It is called a ‘virtual’ photon because it is not detectable in a laboratory. 

Sketch a Feynman diagram to show electrostatic repulsion between two electrons.

2b3 marks

Explain why virtual photons cannot be detected in a laboratory but are nonetheless required by particle physics.

2c3 marks

The unfinished Feynman diagram in Figure 1 shows the interaction between a proton and an anti-neutrino.

2-3-s-q--q2c-hard-aqa-a-level-physics

Complete the Feynman diagram shown in Figure 1.

2d3 marks

The neutron-neutrino interaction can be expressed in a similar way to the Feynman diagram in Figure 1. 

Describe the changes to the Feynman diagram in Figure 1 that would show the neutron-neutrino interaction.

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3a3 marks

Exchange particles are theoretical objects that are used to explain how particles interact with each other. 

One observation that is explained by exchange particles is the fact that the weak nuclear force acts over a much shorter distance than the strong nuclear force.

Explain two differences between the relevant exchange particles that account for this observation.

3b3 marks

The strong interaction between a K particle, which has a strangeness S = –1, and a proton p is shown below:

            K to the power of minus space plus space p space rightwards arrow space K to the power of 0 space plus space K to the power of plus space plus space X 

Deduce the quark composition of X.

3c4 marks

Figure 1 shows a possible mechanism for the interaction between the negative kaon and proton. The exchange particle involved in this reaction is the gluon, g.

 2-3-s-q--q3c-hard-aqa-a-level-physics

Figure 1

Complete the Feynman diagram for the strong interaction in part (b), in terms of the quarks involved.

Do not include any spectator quarks.

3d4 marks

There are other possible outcomes for interaction between the Kand the proton p. Sometimes they interact weakly, with a neutron among only two reaction products.

Discuss this possible interaction, including an appropriate equation.

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4a3 marks

Annihilation is a type of particle interaction during which a colliding particle x and anti-particle x with bar on top convert their masses into pure energy. This energy is radiated by at least two photons gamma . 

The Feynman diagram for such a process is shown in Figure 1

2-3-s-q--q1a-answer-hard-aqa-a-level-physics

Explain why at least two photons result from annihilation.

4b3 marks

Pair production, the opposite process to annihilation, is the creation of a particle and anti-particle pair from the energy carried by a photon.

Sketch a Feynman diagram that represents pair production from a single photon.

4c3 marks

State and explain whether the photon in part (b) can be classified as a virtual photon.

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