Exploring the Structure of Matter (Edexcel International A Level (IAL) Physics): Exam Questions

In 1931, Sloan and Lawrence built a linear accelerator (linac) with several drift tubes.

They used the linac to accelerate mercury ions up to energies of 1.26 MeV. The behaviour of the particles was non-relativistic.

The kinetic energy of a non-relativistic particle of mass m with momentum p is given by

         $E_k=\frac{p^2}{2m}$

Derive this formula.

A mercury ion with kinetic energy 6.42 × 10^–15 J leaves a drift tube, as shown.

Calculate the momentum of the mercury ion when it reaches the next drift tube.    

mass of mercury ion = 3.32 × 10^–25 kg    

charge of mercury ion = 1.60 × 10^–19 C    

electric field strength between drift tubes = 7.64 × 10⁶ Vm^–1

distance between drift tubes = 5.50 × 10^–3 m

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

In 1932, Carl Anderson published this photograph of a track in a cloud chamber. The cloud chamber contained a lead plate. There was a magnetic field perpendicular to the plane of the track.

The photograph shows the track of a positron from cosmic rays and is the first photographic record of the existence of an antiparticle.

State the properties of a positron that show it is the antiparticle to the electron.

Deduce the direction of the magnetic field.

Direction of magnetic field = .........................................

In the upper part of the photograph the positron had an energy of 23 MeV.  

i) Show that the positron must have been travelling at a relativistic speed. Assume that all of its energy is kinetic energy.

   (3)

ii) For relativistic particles such as this positron, momentum obeys the relationship

E = pc

where E = particle energy, p = particle momentum and c = speed of light.

Determine the magnetic flux density of the magnetic field.

radius of curvature of path = 3.7 cm

Magnetic flux density = .........................................(3)

A positron travelling at a non-relativistic speed of 1.5 × 10⁷ m s⁻¹ collides with an electron travelling at the same speed in the opposite direction. This collision results in the production of gamma radiation.

Calculate the frequency of the gamma radiation produced.

Frequency = ..........................................

The ${\mathrm{\pi }}^{-}$ particle is a meson of mass $139.57{\text{ MeV/c}}^2$. It decays via the weak interaction, producing a muon and a neutrino.

The table shows the properties of two quarks.

(i) Give the quark structure of a ${\mathrm{\pi }}^{-}$ particle.

[1]

(ii) Complete the particle equation for this decay.

${\mathrm{\pi }}^{-}\to$

[2]

Energy and momentum must be conserved in this decay.

Explain how two other conservation laws apply to this decay.

Calculate the mass, in kg, of the ${\mathrm{\pi }}^{-}$ particle.

Pions are produced in the upper atmosphere when cosmic rays, consisting mainly of high-energy protons, collide with nuclei.

Explain why a single cosmic ray could lead to the creation of several pions.

The muons produced from the decay of these pions travel towards the Earth's surface at a velocity of $0.99 c$. The average lifetime for muons at rest is $2.2\times {10}^{-6}\text{ s}$, yet muons produced at a height of $10\text{ km}$ are found in significant numbers at sea level.

Explain whether this observation is consistent with ideas from relativity. Your answer should include a calculation.

A hospital radiotherapy unit uses a linear accelerator (linac) to produce beams of high-energy electrons.

The diagram shows the initial section of a linac. The electron source is a metal disc.

Describe how a metal disc can be made to emit electrons.

Each electron leaves the linac with a kinetic energy of $8.0\times {10}^{-12}\text{ J}$.

Calculate the total potential difference through which each electron is accelerated.

Explain how the linac produces a beam of high-energy electrons.