Exploring the Structure of Matter (Edexcel A Level Physics)

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3 marks

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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13 marks

Muons are produced from the decay of pions in the upper atmosphere.
An example of this decay is given by the equation
$π^{-} \to μ^{-} + {\bar{v}}_{μ}$

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.

$π^{-}$	$μ^{-}$	$v_{μ}$
140	106	≈ 0

Explain why the total kinetic energy of the products of this decay is approximately 34 MeV. Assume the $π^{-}$ stationary.

(2)

iii)

State which two conservation laws could be used to calculate the kinetic energy of the

μ^{-}

and the

{\bar{v}}_{μ}

, just after the decay of the

π^{-}

(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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3 marks

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.

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

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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4 marks

A plan view of the arrangement is shown.

q14b-nov-2020-9ph0-01-edexcel-as-a-level-phy

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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