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PHYSICS, M8 2025 HSC 31

Experiments have been carried out by scientists to investigate cathode rays.

Assess the contribution of the results of these experiments in developing an understanding of the existence and properties of electrons.   (5 marks)

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Judgment Statement

  • The cathode ray experiments were highly valuable in establishing both the existence and properties of electrons through definitive experimental evidence and quantitative measurements.

Demonstrating Particle Nature

  • Electric field deflection experiments produced significant results by proving cathode rays were negatively charged particles rather than electromagnetic radiation.
  • This was highly effective because it eliminated the competing theory that cathode rays were electromagnetic waves, since waves are not deflected by electric fields.
  • The consistent deflection pattern across many experiments provided strong evidence for the particle nature of electrons.

Quantifying Electron Properties

  • By adjusting electric and magnetic field strengths within experiments, the charge-to-mass ratio of the electron was determined.
  • This measurement proved highly effective as it provided the first quantitative property of electrons.
  • The e/m ratio demonstrated considerable value by revealing electrons were much lighter than atoms, indicating subatomic particles existed.

Overall Assessment

  • Assessment reveals these experiments achieved major significance in atomic theory development.
  • The combined results produced measurable, reproducible data that definitively established electrons as fundamental charged particles with specific properties.
  • Overall, these contributions proved essential for understanding atomic structure.

 
Other answers could include:

  • By using electrodes made of different materials, Thomson was able to deduce that the cathode rays’ properties were independent of the source of the electrons and hence that they were a constituent of atoms themselves rather than being a product of the cathode ray.
  • Cathode rays were passed through thin metal foils and the analysis of this behaviour allowed scientists (Lenard/Hertz) to deduce that the electrons had mass.
  • Crookes’ observation that cathode rays travelled in straight lines and cast sharp shadows from which he deduced that the rays were particles and not waves (which would have shown diffraction effects).
Show Worked Solution

Judgment Statement

  • The cathode ray experiments were highly valuable in establishing both the existence and properties of electrons through definitive experimental evidence and quantitative measurements.

Demonstrating Particle Nature

  • Electric field deflection experiments produced significant results by proving cathode rays were negatively charged particles rather than electromagnetic radiation.
  • This was highly effective because it eliminated the competing theory that cathode rays were electromagnetic waves, since waves are not deflected by electric fields.
  • The consistent deflection pattern across many experiments provided strong evidence for the particle nature of electrons.

Quantifying Electron Properties

  • By adjusting electric and magnetic field strengths within experiments, the charge-to-mass ratio of the electron was determined.
  • This measurement proved highly effective as it provided the first quantitative property of electrons.
  • The e/m ratio demonstrated considerable value by revealing electrons were much lighter than atoms, indicating subatomic particles existed.

Overall Assessment

  • Assessment reveals these experiments achieved major significance in atomic theory development.
  • The combined results produced measurable, reproducible data that definitively established electrons as fundamental charged particles with specific properties.
  • Overall, these contributions proved essential for understanding atomic structure.

 
Other answers could include:

  • By using electrodes made of different materials, Thomson was able to deduce that the cathode rays’ properties were independent of the source of the electrons and hence that they were a constituent of atoms themselves rather than being a product of the cathode ray.
  • Cathode rays were passed through thin metal foils and the analysis of this behaviour allowed scientists (Lenard/Hertz) to deduce that the electrons had mass.
  • Crookes’ observation that cathode rays travelled in straight lines and cast sharp shadows from which he deduced that the rays were particles and not waves (which would have shown diffraction effects).

PHYSICS, M8 2023 HSC 33

Consider the following statement.

The interaction of subatomic particles with fields, as well as with other types of particles and matter, has increased our understanding of processes that occur in the physical world and of the properties of the subatomic particles themselves.

Justify this statement with reference to observations that have been made and experiments that scientists have carried out.   (9 marks)

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Thomson’s Experiment:

  • Thomson’s experiment tested the interaction of cathode rays (which he discovered were negatively charged subatomic particles and named them electrons) with electric and magnetic fields to determine the charge to mass ratio (\(\dfrac{q}{m}\)) of the electrons.
  • Using both the electric and magnetic fields, Thomson balanced the forces to ensure the cathode rays travelled through undeflected. Thus:
  •    \(F_E = F_B \ \ \Rightarrow \ \ qE=qvB \ \ \Rightarrow \ \ v=\dfrac{E}{B}\)
  • Using the magnetic field and known velocity, the cathode rays travelled in a circular path due to their negative charges interacting with the magnetic field. Thus:
  •    \(F_c=F_B\ \ \Rightarrow \ \ \dfrac{mv^2}{r}=qvB \ \ \Rightarrow \ \ \dfrac{q}{m}=\dfrac{v}{Br}\)
  • The charge to mass ratio was determined to be 0.77 \(\times\) 10\(^{11}\) Ckg\(^{-1}\) and was \(\dfrac{1}{1800}\) times smaller than the charge to mass ratio of the proton. The number was also the same regardless of the metal cathode used, thus Thomson determined this particle was a fundamental constitute of all matter. 
  • Therefore, the statement is true as the observations and experiment undertaken by Thomson using the interactions of particles and fields led to a greater understanding of the electrons. 

Chadwick’s Experiment:

  • In Chadwick’s experiment, he irradiated beryllium with alpha particles which emitted a deeply penetrating radiation with neutral charge. When this particle was directed into paraffin wax, protons were emitted and detected on a screen. 
  • Using the Laws of conservation of energy and momentum, Chadwick proposed the idea of a neutral particle and named it the neutron. He determined that the mass of this particle must be slightly greater than the mass of the proton.
  • Therefore, Chadwick’s observations of the neutrons led to a greater understanding of the properties of the particle, thus justifying the statement above.  

Observations using particle accelerators:

  • Particle accelerators have led to many new scientific discoveries as a result of the interaction of particles with fields and particle-particle interactions.
  • Scientists have come to a greater understanding of quarks and other subatomic particles within the standard model of matter and processes of the physical world including decay trails and momentum dilation.
  • The Large Hadron Collider (LHC) can accelerate particles close to the speed of light using electric and magnetic fields. When particles collide, the kinetic energy is converted into mass using Einstein’s equation  \(E=mc^2\).
  • The new particles formed as a result of these collisions led to the development of the standard model and increased scientific understanding of subatomic particles including up and down quarks, W/Z bosons and the Higgs Boson.
  • These subatomic particles have very short lifetimes before decaying into more stable particles. Our knowledge of them is primarily from studying their decay properties which has led to a greater understanding of particle decay trails.
  • Observations of interactions within particles accelerators has also increased the scientific understanding of momentum dilation. As particles reach relativistic speeds, a greater force is required to accelerate them than classical physics predicts which is due to mass and momentum dilation. 

Other Answers could include:

  • Millikan’s Oil drop experiment.
  • The photoelectric effect.
  • Geiger Marsden experiment.
  • Davisson Germer experiment.
  • Observations of Muons.
Show Worked Solution

One (of many) exemplar responses.

Thomson’s Experiment:

  • Thomson’s experiment tested the interaction of cathode rays (which he discovered were negatively charged subatomic particles and named them electrons) with electric and magnetic fields to determine the charge to mass ratio (\(\dfrac{q}{m}\)) of the electrons.
  • Using both the electric and magnetic fields, Thomson balanced the forces to ensure the cathode rays travelled through undeflected. Thus:
  •    \(F_E = F_B \ \ \Rightarrow \ \ qE=qvB \ \ \Rightarrow \ \ v=\dfrac{E}{B}\)
  • Using the magnetic field and known velocity, the cathode rays travelled in a circular path due to their negative charges interacting with the magnetic field. Thus:
  •    \(F_c=F_B\ \ \Rightarrow \ \ \dfrac{mv^2}{r}=qvB \ \ \Rightarrow \ \ \dfrac{q}{m}=\dfrac{v}{Br}\)
  • The charge to mass ratio was determined to be 0.77 \(\times\) 10\(^{11}\) Ckg\(^{-1}\) and was \(\dfrac{1}{1800}\) times smaller than the charge to mass ratio of the proton. The number was also the same regardless of the metal cathode used, thus Thomson determined this particle was a fundamental constitute of all matter. 
  • Therefore, the statement is true as the observations and experiment undertaken by Thomson using the interactions of particles and fields led to a greater understanding of the electrons.

Chadwick’s Experiment:

  • In Chadwick’s experiment, he irradiated beryllium with alpha particles which emitted a deeply penetrating radiation with neutral charge. When this particle was directed into paraffin wax, protons were emitted and detected on a screen. 
  • Using the Laws of conservation of energy and momentum, Chadwick proposed the idea of a neutral particle and named it the neutron. He determined that the mass of this particle must be slightly greater than the mass of the proton.
  • Therefore, Chadwick’s observations of the neutrons led to a greater understanding of the properties of the particle, thus justifying the statement above.  

Observations using particle accelerators:

  • Particle accelerators have led to many new scientific discoveries as a result of the interaction of particles with fields and particle-particle interactions.
  • Scientists have come to a greater understanding of quarks and other subatomic particles within the standard model of matter and processes of the physical world including decay trails and momentum dilation.
  • The Large Hadron Collider (LHC) can accelerate particles close to the speed of light using electric and magnetic fields. When particles collide, the kinetic energy is converted into mass using Einstein’s equation  \(E=mc^2\).
  • The new particles formed as a result of these collisions led to the development of the standard model and increased scientific understanding of subatomic particles including up and down quarks, W/Z bosons and the Higgs Boson.
  • These subatomic particles have very short lifetimes before decaying into more stable particles. Our knowledge of them is primarily from studying their decay properties which has led to a greater understanding of particle decay trails.
  • Observations of interactions within particles accelerators has also increased the scientific understanding of momentum dilation. As particles reach relativistic speeds, a greater force is required to accelerate them than classical physics predicts which is due to mass and momentum dilation. 

Other Answers could include:

  • Millikan’s Oil drop experiment.
  • The photoelectric effect.
  • Geiger Marsden experiment.
  • Davisson Germer experiment.
  • Observations of Muons.
♦♦ Mean mark 45%.

PHYSICS, M8 EQ-Bank 2 MC

After DC voltage was applied to an apparatus containing hydrogen gas, the hydrogen separated into streams of oppositely charged particles.

What could be concluded from this observation?

  1. Hydrogen gas conducts electricity.
  2. Hydrogen is the simplest element.
  3. Hydrogen atoms have components.
  4. Hydrogen atoms have a neutral charge.
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`C`

Show Worked Solution
  • The separation shows that hydrogen atoms contain both positive (protons) and negative (electrons) components.

`=>C`

PHYSICS, M8 2019 HSC 32

Describe how specific experiments have contributed to our understanding of the electron and ONE other fundamental particle.   (5 marks)

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Millikan’s Oil Drop Experiment:

  • Millikan’s oil drop experiment involved first measuring the terminal velocity of charged oil droplets in a gravitational field and calculating their mass.
  • An electric field was applied to balance the gravitational field, allowing Millikan to find the electric force and hence, charge on an oil droplet.
  • This allowed him to find the charge on an electron as the smallest difference in charges between two oil drops.

Linear accelerator experiment discovering quarks:

  • An experiment involved using a linear accelerator to speed up and fire a beam of electrons at protons. The scattering pattern of the electrons was analysed and was consistent with protons having an internal structure with both positive and negative charges.
  • This contributed to our understanding of the existence of quarks. 

Other possible answers could include:

  • Thomson’s experiment showing the mass to charge ratio of an electron.
  • Experiments involving synchrotrons discovering particles predicted by the standard model of matter, such as the Higgs-Boson.
Show Worked Solution

Millikan’s Oil Drop Experiment:

  • Millikan’s oil drop experiment involved first measuring the terminal velocity of charged oil droplets in a gravitational field and calculating their mass.
  • An electric field was applied to balance the gravitational field, allowing Millikan to find the electric force and hence, charge on an oil droplet.
  • This allowed him to find the charge on an electron as the smallest difference in charges between two oil drops.

Linear accelerator experiment discovering quarks:

  • An experiment involved using a linear accelerator to speed up and fire a beam of electrons at protons. The scattering pattern of the electrons was analysed and was consistent with protons having an internal structure with both positive and negative charges.
  • This contributed to our understanding of the existence of quarks. 

Other possible answers could include:

  • Thomson’s experiment showing the mass to charge ratio of an electron.
  • Experiments involving synchrotrons discovering particles predicted by the standard model of matter, such as the Higgs-Boson.

♦♦ Mean mark 43%.

PHYSICS, M8 2021 HSC 23

Describe how Millikan and Thomson each used fields to determine properties of the electron.   (4 marks)

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Thomson used an electric field to accelerate electrons. He deflected these electrons using a magnetic field then balanced the force on these electrons using a second electric field, allowing him to calculate the charge to mass ratio of an electron.

Millikan used electric fields to suspend oil droplets by balancing their weight due to Earth’s electric field, allowing him to calculate the charge of an electron.

Show Worked Solution

Thomson used an electric field to accelerate electrons. He deflected these electrons using a magnetic field then balanced the force on these electrons using a second electric field, allowing him to calculate the charge to mass ratio of an electron.

Millikan used electric fields to suspend oil droplets by balancing their weight due to Earth’s electric field, allowing him to calculate the charge of an electron.