Applications of Conservation Laws

How quark character changes in β⁻ and β⁺ decay at the fundamental level Applying conservation of charge to determine if interactions are possible Applying conservation of baryon number and lepton number to validate interactions Applying conservation of strangeness to distinguish strong from weak interactions Using all conservation laws together to assess whether a given particle interaction can occur

A-Level Physics AQA 9 questions 9 mins

Preview Questions

Q1. In β⁺ decay, which quark change occurs and which exchange particle is involved?

Multiple Choice · 1 point

· A down quark changes to an up quark via a W⁻ boson
· An up quark changes to a down quark via a W⁺ boson
· A down quark changes to an up quark via a W⁺ boson
· An up quark changes to a strange quark via a W⁺ boson

Q2. Which of the following correctly describes the quark change in β⁻ decay?

Multiple Choice · 1 point

· u → d + W⁺
· d → u + W⁻
· u → s + W⁻
· s → d + W⁺

Q3. Is the following interaction possible? p → n + e⁺ + vₑ

Multiple Choice · 1 point

· No - charge is not conserved
· No - baryon number is not conserved
· No - lepton number is not conserved
· Yes - all conservation laws are satisfied

Q4. Is the following interaction possible? n → p + e⁻

Multiple Choice · 1 point

· Yes - charge and baryon number are both conserved
· No - charge is not conserved
· No - lepton number is not conserved
· No - baryon number is not conserved

Q5. A particle interaction produces a kaon with strangeness S = +1 and no other strange particles. Which interaction was responsible?

Multiple Choice · 1 point

· Strong interaction, since strangeness is conserved
· Weak interaction, since strangeness can change by ±1
· Electromagnetic interaction, since photons are involved
· Strong interaction, since kaons are hadrons

Q6. Which of the following correctly identifies all the quantities that must be conserved in every particle interaction?

Multiple Choice · 1 point

· Charge, baryon number and strangeness only
· Charge, lepton number and strangeness only
· Charge, baryon number, lepton number, energy and momentum
· Baryon number, lepton number and strangeness only

Q7. Consider the interaction: π⁻ + p → K⁰ + Λ⁰, where K⁰ has strangeness S = +1 and Λ⁰ has strangeness S = -1. Is strangeness conserved?

Multiple Choice · 1 point

· No - strangeness changes by +1
· No - strangeness changes by -1
· Yes - total strangeness is 0 on both sides
· Yes - but only because this is a weak interaction

Q8. A muon decays as: μ⁻ → e⁻ + X + Y. What are the identities of X and Y needed to conserve lepton number?

Multiple Choice · 1 point

· X = vₑ, Y = v̄μ
· X = v̄ₑ, Y = vμ
· X = vμ, Y = vₑ
· X = v̄μ, Y = v̄ₑ

Q9. Which conservation law rules out the following decay: Λ⁰ → p + p̄, where Λ⁰ has baryon number +1?

Multiple Choice · 1 point

· Conservation of charge
· Conservation of lepton number
· Conservation of strangeness
· Conservation of baryon number

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