Physics (Version 8.4)

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Unit 4

Understand how Physics works

Rationale/Aims

Physics is a fundamental science that endeavours to explain all the natural phenomena that occur in the universe. Its power lies in the use of a comparatively small number of assumptions, models, laws and theories to explain a wide range of phenomena, from the incredibly small to the incredibly large.

Structure of Physics

In Physics, students develop their understanding of the core concepts, models and theories that describe, explain and predict physical phenomena.

Links to Foundation to Year 10

The Physics curriculum continues to develop student understanding and skills from across the three strands of the F-10 Australian Curriculum: Science. In the Science Understanding strand, the Physics curriculum draws on knowledge and understanding from across the four sub-strands of Biological, Physical, Chemical and Earth and Space Sciences.

Representation of Cross-curriculum priorities

While the significance of the cross-curriculum priorities for Physics varies, there are opportunities for teachers to select contexts that incorporate the key concepts from each priority.

Achievement standards

Unit 4: Revolutions in modern physics

Unit 4: Revolutions in modern physics Description

The development of quantum theory and the theory of relativity fundamentally changed our understanding of how nature operates and led to the development of a wide range of new technologies, including technologies that revolutionised the storage, processing and communication of information. In this unit, students examine observations of relative motion, light and matter that could not be explained by existing theories, and investigate how the shortcomings of existing theories led to the development of the special theory of relativity and the quantum theory of light and matter. Students evaluate the contribution of the quantum theory of light to the development of the quantum theory of the atom, and examine the Standard Model of particle physics and the Big Bang theory.

Contexts that could be investigated in this unit include technologies such as GPS navigation, lasers, modern electric lighting, medical imaging, nanotechnology, semiconductors, quantum computers and particle accelerators; and related areas of science such as space travel, the digital revolution and the greenhouse effect.

Through the investigation of appropriate contexts, students explore the ways in which these models and theories, and associated technologies, have developed over time and through interactions with social, economic, cultural and ethical considerations. They investigate the ways in which science contributes to contemporary debate about local, regional and international issues, including evaluation of risk and action for sustainability, and recognise the limitations of science to provide definitive answers in different contexts.

Through investigation, students apply their understanding of relativity, black body radiation, wave/particle duality, and the quantum theory of the atom, to make and/or explain observations of a range of phenomena such as atomic emission and absorption spectra, the photoelectric effect, lasers, and Earth’s energy balance. They continue to develop skills in planning, conducting and interpreting the results of investigations, in synthesising evidence to support conclusions, and in recognising and defining the realm of validity of physical theories and models.

Unit 4: Revolutions in modern physics Learning Outcomes

By the end of this unit, students:

understand the consequences for space and time of the equivalence principle for inertial frames of reference
understand how the quantum theory of light and matter explains blackbody radiation, the photoelectric effect, and atomic emission and absorption spectra
understand how the Standard Model explains the nature of and interaction between the fundamental particles that form the building blocks of matter
understand how models and theories have developed over time, and the ways in which physical science knowledge and associated technologies interact with social, economic, cultural and ethical considerations
use science inquiry skills to design, conduct, analyse and evaluate investigations into frames of reference, diffraction, black body and atomic emission spectra, the photoelectric effect, and photonic devices, and to communicate methods and findings
use algebraic and graphical models to solve problems and make predictions related to the theory and applications of special relativity, quantum theory and the Standard Model
evaluate the experimental evidence that supports the theory of relativity, wave-particle duality, the Bohr model of the atom, the Standard Model, and the Big Bang theory
communicate physics understanding using qualitative and quantitative representations in appropriate modes and genres.

Unit 4: Revolutions in modern physics Content Descriptions

Science Inquiry Skills

Identify, research and construct questions for investigation; propose hypotheses; and predict possible outcomes (ACSPH114)

Design investigations, including the procedure to be followed, the materials required, and the type and amount of primary and/or secondary data to be collected; conduct risk assessments; and consider research ethics (ACSPH115)

Conduct investigations, including use of simulations and manipulation of spectral devices, safely, competently and methodically for the collection of valid and reliable data (ACSPH116)

Represent data in meaningful and useful ways, including using appropriate SI units, symbols and significant figures; organise and analyse data to identify trends, patterns and relationships; identify sources of uncertainty and techniques to minimise these uncertainties; utilise uncertainty and percentage uncertainty to determine the cumulative uncertainty resulting from calculations, and evaluate the impact of measurement uncertainty on experimental results; and select, synthesise and use evidence to make and justify conclusions (ACSPH117)

Interpret a range of scientific and media texts, and evaluate processes, claims and conclusions by considering the quality of available evidence; and use reasoning to construct scientific arguments (ACSPH118)

Select, construct and use appropriate representations, including text and graphic representations of empirical and theoretical relationships, simulations, simple reaction diagrams and atomic energy level diagrams, to communicate conceptual understanding, solve problems and make predictions (ACSPH119)

Select, use and interpret appropriate mathematical representations, including linear and non-linear graphs and algebraic relationships representing physical systems, to solve problems and make predictions (ACSPH120)

Communicate to specific audiences and for specific purposes using appropriate language, nomenclature, genres and modes, including scientific reports (ACSPH121)

Science as a Human Endeavour (Units 3 & 4)

ICT and other technologies have dramatically increased the size, accuracy and geographic and temporal scope of datasets with which scientists work (ACSPH122)

Models and theories are contested and refined or replaced when new evidence challenges them, or when a new model or theory has greater explanatory power (ACSPH123)

The acceptance of science understanding can be influenced by the social, economic and cultural context in which it is considered (ACSPH124)

People can use scientific knowledge to inform the monitoring, assessment and evaluation of risk (ACSPH125)

Science can be limited in its ability to provide definitive answers to public debate; there may be insufficient reliable data available, or interpretation of the data may be open to question (ACSPH126)

International collaboration is often required when investing in large-scale science projects or addressing issues for the Asia-Pacific region (ACSPH127)

Scientific knowledge can be used to develop and evaluate projected economic, social and environmental impacts and to design action for sustainability (ACSPH128)

Science Understanding

Special relativity

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Development of the special theory of relativity

Many scientists, including Albert Michelson, Hendrik Lorentz and Henri Poincaré, contributed to the development of the special theory of relativity. Lorentz’s Transformation and his ideas about the aether initially explained the Doppler effect. They were improved upon by the next generation of scientists developing theories about electromagnetic mass and ideas about inertial frames of reference and relative motion. Albert Einstein’s work on special relativity built upon the work of scientists such as Maxwell and Lorentz, while subsequent studies by Max Planck, Hermann Minkowski and others led to the development of relativistic theories of gravitation, mass-energy equivalence and quantum field theory. The Michelson-Morley and Fizeau experiments provided evidence for the special theory of relativity (ACSPH123).

Ring laser gyroscopes and navigation

Ring laser gyroscopes (RLG) are inertial guidance systems that do not rely on signals from an external source but from instruments on board a moving object. RLGs use small differences in the time it takes light to travel around the ring in two directions, known as the Sagnac effect. RLGs have many advantages over other systems: they are highly accurate, have no moving parts, are compact and lightweight, and do not resist changes to their orientation (ACSPH122). RLGs are commonly used in aircraft for accurate navigation and have military applications in helicopters, ships, submarines and missiles.

Nuclear reactors

Special relativity leads to the idea of mass-energy equivalence, which has been applied in nuclear fission reactors. Nuclear reactors are most commonly used for power generation, propulsion and scientific research. Research reactors have resulted in advances in areas such as medicine and materials testing and fabrication through provision of nuclear isotopes for industrial and medical applications. Although nuclear reactors provide a range of benefits, there is considerable public concern over safety and security issues (ACSPH124). Data from the nuclear industry indicates that nuclear power reactors pose an acceptable risk to public safety and that much has been done to limit that risk. However, other groups argue that such a risk is not acceptable, and, even if no accidents occur, storage of the radioactive waste produced from nuclear facilities remains a safety concern (ACSPH126).

Mathematical representations and relationships

\(\mathrm t\;=\frac{{\mathrm t}_\mathrm o}{\sqrt[{}]{\left(1-\frac{\mathrm v^2}{\mathrm c^2}\right)}}\)

\(\mathrm t\;=\) time interval in the moving frame as measured by the observer in the proper frame, \({\mathrm t}_\mathrm o=\) proper time interval (time interval for a clock at rest in the observer’s frame), \(\mathrm v\;=\) relative speed of the two inertial frames, \(\mathrm c\;=\) speed of light in a vacuum \(\left(3\;\times10^8\;\text{m }\text{s}^{-1}\right)\)

\(\mathrm l=\;{\mathrm l}_\mathrm o\sqrt[{}]{\left(1-\frac{\mathrm v^2}{\mathrm c^2}\right)}\)

\(\mathrm l=\;\) length interval in the frame moving at velocity \(\mathrm v\) with respect to the observer, \({\mathrm l}_\mathrm o=\;\) lo= proper length (length in a frame at rest with respect to the observer), \(\mathrm c\;=\) speed of light \(\left(3\;\times10^8\;\text{m }\text{s}^{-1}\right)\)

\({\mathrm p}_\mathrm v=\frac{\mathrm m\mathrm v}{\sqrt[{}]{\left(1-\frac{\mathrm v^2}{\mathrm c^2}\right)}}\)

\({\mathrm p}_\mathrm v=\) relativistic momentum for an object moving with velocity, \(\mathrm v\) with respect to the observer, \(\mathrm m\) \(=\) mass, \(\mathrm c\;=\) speed of light

\(\left(3\;\times10^8\;\text{m }\text{s}^{-1}\right)\)

\(\operatorname\Delta\mathrm E=\mathrm\Delta\mathrm m\mathrm c^2\)

\(\mathrm\Delta\mathrm E=\) change in energy, \(\;\mathrm\Delta\mathrm m=\) change in mass, \(\;\mathrm c=\;\) c= speed of light

\(\left(3\;\times10^8\;\text{m }\text{s}^{-1}\right)\)

Observations of objects travelling at very high speeds cannot be explained by Newtonian physics (for example, the dilated half-life of high-speed muons created in the upper atmosphere, and the momentum of high speed particles in particle accelerators) (ACSPH129)

Einstein’s special theory of relativity predicts significantly different results to those of Newtonian physics for velocities approaching the speed of light (ACSPH130)

The special theory of relativity is based on two postulates: that the speed of light in a vacuum is an absolute constant, and that all inertial reference frames are equivalent (ACSPH131)

Motion can only be measured relative to an observer; length and time are relative quantities that depend on the observer’s frame of reference (ACSPH132)

Relativistic momentum increases at high relative speed and prevents an object from reaching the speed of light (ACSPH133)

The concept of mass-energy equivalence emerged from the special theory of relativity and explains the source of the energy produced in nuclear reactions (ACSPH134)

Quantum theory

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Development of the quantum model

Max Planck and Einstein were the first to describe light and energy as being quantised, a finding that led to light being described as spatially quantised photons of energy. The Bohr model of the atom was built on this quantised description of light energy and Rutherford’s nuclear model. The Bohr model was a quantum-based modification to Rutherford’s model and was rapidly accepted due to its ability to explain the emission lines of atomic hydrogen. Prior to Bohr’s model, the Rydberg formula describing the wavelengths of spectral lines of many chemical elements was known but could not be explained. A more elaborate quantum mechanical model of the atom, however, was required to explain other observations made about atoms. The quantum mechanical model of the atom uses quantum theory and describes electron orbitals that can be used to calculate the probability of finding an electron at a specific point (ACSPH123).

Black body radiation and the greenhouse effect

All objects in the universe, including the sun and Earth, emit black body radiation. The natural temperature of Earth can be predicted using the Stefan-Boltzmann black body radiation equation which assumes there is a balance between incoming and outgoing radiation. The true temperature is significantly higher due to the absorption of emitted black body radiation from the surface by molecules in the atmosphere (the greenhouse effect). Models of Earth’s energy balance enable scientists to monitor changes in global temperature, assess the evidence for changes in climate due to the enhanced greenhouse effect, and evaluate the risk posed by anthropogenic climate change (ACSPH125). Further development of models of Earth’s energy dynamics and climate change enables scientists to more accurately predict the scenarios that will result in global warming, the time frames involved, and the likely impacts of these changes (ACSPH128).

Mathematical representations and relationships

\(\mathrm E=\mathrm h\mathrm f\)

\(\mathrm E\;=\) energy of photon, \(\mathrm f\;=\) frequency, \(\mathrm h\;=\)

\(\left(6.626\;\times\;10^{-34}\;\mathrm J\;\mathrm s\right)\)

\({\mathrm\lambda}_{\mathrm m\mathrm a\mathrm x}\;=\frac{\mathrm b}{\mathrm T}\)

\({\mathrm\lambda}_{\mathrm m\mathrm a\mathrm x}=\;\) peak wavelength, \(\mathrm T\;=\;\) absolute temperature, \(\mathrm b\;=\) Wien’s displacement constant \(\text{(2.898 × }10^{-3}\;\text{m K)}\)

\({\mathrm E}_\mathrm k=\mathrm h\mathrm f-\;\mathrm W\)

\({\mathrm E}_\mathrm k=\;\) Ek= kinetic energy of photoelectron, \(\mathrm h\mathrm f\;=\) energy of incident photon, \(\;\mathrm W\;=\;\) work function of the material

\(\mathrm\lambda=\frac{\mathrm h}{\mathrm p}\)

\(\mathrm\lambda=\) wavelength associated with particle, \(\mathrm p\;=\) momentum of particle, \(\mathrm h\;=\) Planck’s constant \(\left(6.626\;\times\;10^{-34}\;\mathrm J\;\mathrm s\right)\)

\(\mathrm n\mathrm\lambda=2\mathrm\pi\mathrm r\)

\(\mathrm n\;=\) an integer 1, 2, 3, 4... , \(\mathrm\lambda=\)wavelength of electron, \(\mathrm r\;=\) orbital radius of electron

\(\mathrm m\mathrm v\mathrm r=\frac{\mathrm n\mathrm h}{2\mathrm\pi}\)

\(\mathrm m\;=\) mass of electron, \(\mathrm v\;=\) velocity of electron, \(\mathrm r\;=\) orbital radius of electron, \(\mathrm n\;=\) an integer 1, 2, 3, 4, etc., \(\mathrm h\;=\) Planck’s constant \(\left(6.626\;\times\;10^{-34}\;\mathrm J\;\mathrm s\right)\)

\(\frac1{\mathrm\lambda}=\mathrm R\left(\frac1{\mathrm n_\mathrm f^2}-\frac1{\mathrm n_\mathrm i^2}\right)\)

\(\mathrm\lambda=\) wavelength of spectral line, \({\mathrm n}_\mathrm i=\;\) principal quantum number of initial electron state, \(\;{\mathrm n}_\mathrm f=\;\) nf= principal quantum number of final electron state, \(\mathrm R\;=\) Rydberg’s constant \(\text{(1.097 × }10^7\;\text{m}^{-1}\text{)}\)

Atomic phenomena and the interaction of light with matter indicate that states of matter and energy are quantised into discrete values (ACSPH135)

On the atomic level, electromagnetic radiation is emitted or absorbed in discrete packets called photons; the energy of a photon is proportional to its frequency; and the constant of proportionality, Planck’s constant, can be determined experimentally (for example, from the photoelectric effect or the threshold voltage of coloured LEDs) (ACSPH136)

A wide range of phenomena, including black body radiation and the photoelectric effect, are explained using the concept of light quanta (ACSPH137)

Atoms of an element emit and absorb specific wavelengths of light that are unique to that element; this is the basis of spectral analysis (ACSPH138)

The Bohr model of the hydrogen atom integrates light quanta and atomic energy states to explain the specific wavelengths in the hydrogen spectrum and in the spectra of other simple atoms; the Bohr model enables line spectra to be correlated with atomic energy-level diagrams (ACSPH139)

On the atomic level, energy and matter exhibit the characteristics of both waves and particles (for example, Young’s double slit experiment is explained with a wave model but produces the same interference pattern when one photon at a time is passed through the slits) (ACSPH140)

The Standard Model

Examples in context

Support materials only that illustrate some possible contexts for exploring Science as a Human Endeavour concepts in relation to Science Understanding content.

Evidence for the Higgs boson particle

The Higgs boson particle was predicted in the early 1960s by the Standard Model of particle physics. Evidence for the Higgs boson particle would confirm the existence of the Higgs field and help to explain why fundamental particles have mass. Discovery of the particle would guide other theories and discoveries in this field, including validation of the Standard Model, and insights into cosmic inflation and the cosmological constant problem (ACSPH123). Production of the Higgs boson requires an extremely powerful particle accelerator. The Large Hadron Collider at CERN was built to test particle physics theories, and specifically to try to produce and detect the Higgs boson particle. Since the commencement of its operation, previously unobserved particles have been produced (ACSPH123) and most recently a new particle has been observed that is consistent with the theorised Higgs boson particle.

Particle Accelerators

Particle accelerators propel charged particles to high speeds using a combination of electric and magnetic fields. High-energy particle accelerators are used in particle physics research to create and observe particles. These machines have gradually increased in size, complexity and in their ability to accelerate particles to higher speeds, thus increasing scientists’ ability to observe new particles (ACSPH122). More practical uses of particle accelerators include their use in production of radioisotopes for medical treatments and as synchrotron light sources. The construction of the Australian Synchrotron involved collaboration between Australian and New Zealand science organisations, state and federal governments and international organisations and committees including the International Science Advisory Committee and the International Machine Advisory Committee (ACSPH127).

The Big Bang Theory

The Big Bang Theory describes the early development of the universe including the formation of subatomic particles from energy and the subsequent formation of atomic nuclei. There is a variety of evidence that supports the Big Bang Theory including Cosmic Background Radiation, the abundance of light elements and the red shift of light from galaxies that obey Hubble’s Law. Alternate theories exist including the Steady State theory, but the Big Bang Theory is the most widely accepted theory today (ACSPH123). There is opposition to this theory in both scientific and religious communities due to its inability to explain what came before the singularity and because it cannot explain all aspects of the universe as it exists today (ACSPH124).

The Standard Model is based on the premise that all matter in the universe is made up from elementary matter particles called quarks and leptons; quarks experience the strong force, leptons do not (ACSPH141)

The Standard Model explains three of the four fundamental forces (strong, weak and electromagnetic forces) in terms of an exchange of force-carrying particles called gauge bosons; each force is mediated by a different type of gauge boson (ACSPH142)

Reactions between particles can be represented by simple reaction diagrams (ACSPH143)

Lepton number and baryon number are examples of quantities that are conserved in all reactions between particles; conservation laws can be used to support or invalidate proposed reactions (ACSPH144)

Variations of reactions can be found by applying symmetry operations to known reactions. These include reversing the direction of the reaction diagram (time reversal symmetry) and replacing all particles with their antiparticles and vice versa (charge reversal symmetry). Energy and momentum must also be conserved for such a reaction to be possible. (ACSPH145)

High-energy particle accelerators are used to test theories of particle physics including the Standard Model (ACSPH146)

The Standard Model is used to describe the evolution of forces and the creation of matter in the Big Bang theory (ACSPH147)