A LevelPhysicsEdexcelExam Questions8. Nuclear & Particle PhysicsExploring the Structure of Matter

Exploring the Structure of Matter (Edexcel A Level Physics)

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Exploring the Structure of Matter

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1a
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The diagram shows a model used to demonstrate alpha particle scattering. A ball bearing is set rolling on a wooden track. The track is positioned so that the ball bearing rolls onto a metal sheet with a curved surface known as a ʻhillʼ.

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The diagram shows a vertical cross-section through the hill. The surface is curved so that the height of a point h on the curved surface is inversely proportional to the distance r from the centre of the hill.

q14-1-nov-2020-9ph0-01-edexcel-as-a-level-phy

Explain why the hill is suitable as a model for the electric field surrounding the nucleus of an atom.

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1b
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A plan view of the arrangement is shown.

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The wooden track is moved to different positions and the ball bearing is released.

Describe the results of the alpha particle scattering experiment and how these can be demonstrated by moving the wooden track to different positions.

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2a
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At the beginning of the 20th century, Rutherford carried out large-angle alpha particle scattering experiments using gold (Au presubscript 79 presuperscript 197) foil.

The vast majority of the alpha particles went straight through the foil whilst a few were deflected straight back.

Describe how the model of the atom changed, as a consequence of these experiments.

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2b
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In one experiment the alpha particles had an initial energy of 7.7 MeV.

Calculate the distance of closest approach of the alpha particles to the nucleus of a gold atom. Assume that the gold nucleus remains at rest.

Distance of closest approach = .......................................................

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2c
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Rutherford also carried out the experiment with aluminium (Al presubscript 13 presuperscript 27) foil.

The aluminium foil had the same thickness as the gold foil and the alpha particles had the same initial kinetic energy.
The following observations were made.

Observation 1:
The fraction of alpha particles scattered at any particular angle for aluminium foil was always much less than for gold foil.

Observation 2:
The alpha particles scattered from aluminium foil had less kinetic energy than the alpha particles scattered from gold foil.

Explain how these observations can be used to deduce how an aluminium nucleus compares to a gold nucleus.

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3a
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The bubble chamber photograph shows tracks made by a proton and a pion. The proton and pion were both created by the decay of a lambda particle. No other particles were produced.

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*Explain how observations and measurements from the photograph can be used to establish information about the lambda particle.

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3b
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The lambda particle consists of up, down and strange quarks.
Explain how the conservation of charge, baryon number and lepton number apply to the decay of the lambda particle.

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3c
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Write an equation to represent the decay of the lambda (Λ) particle.

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3d
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The rest mass of the lambda particle is 1115 MeV/ c2.

i)
Calculate this mass in kg.

Mass = ....................................................... kg

ii)
The rest mass of a proton is 940 MeV / c2. The rest mass of a pion is 140 MeV / c2.
The kinetic energy of the lambda particle just before decay is 4.95 GeV.
Calculate the total kinetic energy of the proton and pion in MeV.

Total kinetic energy = ....................................................... MeV

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4a
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The discovery of the Higgs particle was an important contribution to our understanding of particle physics.

Describe the standard model for subatomic particles. You should identify the fundamental particles and the composition of the particles we can observe.

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4b
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The mass of the Higgs particle is 2.2× 10–25 kg.

Calculate this mass in GeV/c2





Mass = ........................................... GeV/c2

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4c
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The Higgs particle was discovered using the Large Hadron Collider (LHC) in 2012.
Two beams of very high energy protons, moving in opposite directions, were made to collide.

i)
Explain the need for such high energy collisions.

(3)

ii)
The beams of protons are contained within a ring of superconducting magnets.

Calculate the momentum of a proton in a beam.

(3)

magnetic field strength = 8.3 T
circumference of the ring = 27 km




Momentum = ........................................

iii)
State the total momentum of the products of the collision between the two beams of protons.

(1)


Total momentum = .....................................

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4d
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The LHC accelerates protons until they gain energies of about 7 TeV.

A student used the equation E subscript k space equals fraction numerator p squared over denominator 2 m end fraction to predict the energy of a proton in the beam, using the momentum calculated in (c)(ii), but found the energy was far higher than 7 TeV.

Explain why.

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1a
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A muon (μ) is a lepton with a mass of 106 MeV / c2.

Calculate the mass of a muon in kg.  

      

                                             Mass of muon = ...................................kg

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1b
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Muons are produced from the decay of pions in the upper atmosphere.
An example of this decay is given by the equation
                     straight pi to the power of minus rightwards arrow straight mu to the power of minus plus space straight v with bar on top subscript straight mu

i)
Explain how this decay obeys the laws of conservation of charge, baryon number and lepton number. 

(3)

ii)
The masses of these three particles, in MeV/c2, are given below. 

straight pi to the power of minus straight mu to the power of minus space top enclose straight v subscript straight mu
140 106 ≈ 0

Explain why the total kinetic energy of the products of this decay is approximately 34 MeV. Assume the straight pi to the power of minus stationary. 

(2)

iii)
State which two conservation laws could be used to calculate the kinetic energy of the straight mu to the power of minus and the space v with bar on top subscript mu, just after the decay of the straight pi to the power of minus.  

(2)

iv)
The muons are produced at a height of 10 km in the atmosphere. The velocity of the muons is 0.99 c. The average lifetime for muons is normally 2.2 μs and yet muons produced in the upper atmosphere are found in significant numbers at sea level.

Discuss this apparent anomaly. 

(6)

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