# Year 12 – Nature of light

###### Material moved from options to core syllabus

Electromagnetic Spectrum

Inquiry question: What is light?

Students:

• investigate Maxwell’s contribution to the classical theory of electromagnetism, including:
• unification of electricity and magnetism
• prediction of electromagnetic waves
• prediction of velocity (ACSPH113)
• describe the production of electromagnetic waves and relate these processes qualitatively to the predictions made by Maxwell’s electromagnetic theory (ACSPH112, ACSPH113)
• conduct investigation of historical and contemporary methods used to determine the speed of light and its current relationship to the measurement of time and distance (ACSPH082)
• conduct an investigation to examine a variety of spectra produced by discharge tubes, reflected sunlight or incandescent filaments
• investigate how spectrometry 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

Resource – Maxwell and Electromagnetism – 2 pages

Investigation – Spectroscopy- 3 pages

Resource-Stellar Spectra-5 pages

Light: Wave Model

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

Students:

• conduct investigations to analyse qualitatively the diffraction of light (ACSPH048, ACSPH076)
• conduct investigations to analyse quantitatively the interference of light using double slit apparatus and diffraction gratings $(d\sin{\theta} = m\lambda)$ (ACSPH116, ACSPH117, ACSPH140)
• analyse the experimental evidence that supported the models of light that were proposed by Newton and Huygens (ACSPH050, ACSPH118, ACSPH123)
• conduct investigations quantitatively using the relationship of Malus’s Law $(I = I_{max}\cos{^2\theta})$ for plane polarisation of light, to evaluate the significance of polarisation in developing a model for light (ACSPH050, ACSPH076, ACSPH 120)

Resource – Newton vs Huygens – 2 pages

Light: Quantum Model

Inquiry question: 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?

Students:

• analyse the experimental evidence gathered about black body radiation, including Wein’s Law $\big( \lambda_{max} = \frac{b}{T} \big),$  related to Plank’s contribution to a changed model of light (ACSPH137)
• investigate the evidence from photoelectric effect investigations that demonstrated inconsistency with the wave model for light (ACSPH087, ACSPH123, ACSPH137)
• analyse the photoelectric effect $(E_k = hf - \phi)$ as it occurs in metallic elements by applying the law of conservation of energy and the photon model of light, (ACSPH119)

Light and special relativity

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

Students:

• 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 (ACSPH131)
• investigate the evidence, from Einstein’s thought experiments and subsequent experimental validation, for time dilation $\Bigg( t = \frac{t_{o}}{\sqrt{\big(1-\frac{v^2}{c^2}}\big)} \Bigg)$
• and length contraction $\bigg( l = l_{o}{\sqrt{\big(1-\frac{v^2}{c^2}}\big)} \bigg)$, 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:
• $p_{v} = \frac{mv}{\sqrt{\big( 1-\frac{v^2}{c^2}\big)}}$
• the limitation on the maximum velocity of a particle imposed by special relativity (ACSPH133)
• Use Einstein’s mass-energy equivalence relationship EQN to calculate the energy released by processes in which mass is converted to energy, for example: (ACSPH134)
•
• production of energy by the sun
• particle-antiparticle interactions, e.g. positron-electron annihilation
• combustion of conventional fuel

Resource – Special Relativity – 3 pages

Resource – E=mc2 – 1 page