The Nature of Light

This lesson comprises eight (8) master classes focusing on:

• Wave model of light
• Electromagnetic waves
• Quantisation of energy
• Photon model of light
• Spectroscopy
• Special relativity

Content:

PH12-14

What is light?

• Investigate Maxwell’s contribution to the classical theory of electromagnetism, including:
  • unification of electricity and magnetism
  • prediction of electromagnetic waves
  • prediction of velocity
• Describe the production and propagation of electromagnetic waves and relate these processes qualitatively to the predictions made by Maxwell’s electromagnetic theory
• Conduct investigations of historical and contemporary methods used to determine the speed of light and its current relationship to the measurement of time and distance
• Conduct an investigation to examine a variety of spectra produced by discharge tubes, reflected sunlight or incandescent filaments
• Investigate how spectroscopy can be used to provide information about:
  • the identification of elements
• Investigate how the spectra of stars can provide information on:
  • surface temperature
  • rotational and translational velocity
  • density
  • chemical composition

What evidence supports the classical wave model of light and what predictions can be made using this model?

• Conduct investigations to analyse qualitatively the diffraction of light
• conduct investigations to analyse quantitatively the interference of light using double slit apparatus and diffraction gratings \( d \sin \theta=m \lambda \)
• Analyse the experimental evidence that supported the models of light that were proposed by Newton and Huygens
• Conduct investigations quantitatively using the relationship of Malus’ Law \( I=I_{max} \cos 2 \theta \) for plane polarisation of light, to evaluate the significance of polarisation in developing a model for light

What evidence supports the particle model of light and what are the implications of this evidence for the development of the quantum model of light?

• Analyse the experimental evidence gathered about black body radiation, including Wien’s Law related to Planck's contribution to a changed model of light
  • \( \lambda_{max}=\frac{b}{T} \)
• Investigate the evidence from photoelectric effect investigations that demonstrated inconsistency with the wave model for light
• Analyse the photoelectric effect \( K_{max}=hf− \phi \) as it occurs in metallic elements by applying the law of conservation of energy and the photon model of light

How does the behaviour of light affect concepts of time, space and matter?

• Analyse and evaluate the evidence confirming or denying Einstein’s two postulates:
  • the speed of light in a vacuum is an absolute constant
  • all inertial frames of reference are equivalent
• investigate the evidence, from Einstein’s thought experiments and subsequent experimental validation, for time dilation \( t=\frac{t_0}{\sqrt{(1−\frac{v_2}{c_2})}} \) and length contraction \( l=l_0\sqrt{(1−\frac{v_2}{c_2})} \), and analyse quantitatively situations in which these are observed, for example:
  • observations of cosmic-origin muons at the Earth’s surface
  • atomic clocks (Hafele–Keating experiment)
  • evidence from particle accelerators
  • evidence from cosmological studies
• Describe the consequences and applications of relativistic momentum with reference to:
  • \( p_v=\frac{m_0v}{\sqrt{(1-\frac{v^2}{c^2}}} \)
  • the limitation on the maximum velocity of a particle imposed by special relativity
• Use Einstein’s mass–energy equivalence relationship \( E=mc^2 \) to calculate the energy released by processes in which mass is converted to energy, for example:
  • production of energy by the sun
  • particle–antiparticle interactions, eg positron–electron annihilation
  • combustion of conventional fuel

PH12-1

• Develop and evaluate inquiry questions and hypotheses to identify a concept that can be investigated scientifically, involving primary and secondary data
• Modify questions and hypotheses to reflect new evidence

PH12-2

• Assess risks, consider ethical issues and select appropriate materials and technologies when designing and planning an investigation
• Justify and evaluate the use of variables and experimental controls to ensure that a valid procedure is developed that allows for the reliable collection of data
• Evaluate and modify an investigation in response to new evidence

PH12-3

• Employ and evaluate safe work practices and manage risks
• Use appropriate technologies to ensure and evaluate accuracy
• Select and extract information from a wide range of reliable secondary sources and acknowledge them using an accepted referencing style

PH12-4

• Select qualitative and quantitative data and information and represent them using a range of formats, digital technologies and appropriate media
• Apply quantitative processes where appropriate
• Evaluate and improve the quality of data

PH12-7

• Select and use suitable forms of digital, visual, written and/or oral forms of communication
• Select and apply appropriate scientific notations, nomenclature and scientific language to communicate in a variety of contexts
• Construct evidence-based arguments and engage in peer feedback to evaluate an argument or conclusion