We now turn our attention to the concept of optics which is about the properties and behaviours of electromagnetic radiation, and in particular visible light.
Physical optics deals with the properties of light itself and the behaviour of electromagnetic radiation as it interacts with material. This is in contrast with geometric optics, which is involved in the image producing properties of electromagnetic radiation. This is discussed on the next page.
Physical optics deals with the properties of light itself and the behaviour of electromagnetic radiation as it interacts with material. This is in contrast with geometric optics, which is involved in the image producing properties of electromagnetic radiation. This is discussed on the next page.
1. The Nature of Light - Newton vs Huijgens
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In the 17th Century the nature of light was hotly debated. The English scientist so Isaac Newton proposed a particle model, also referred to as the corpuscular model.
Christiaan Huygens suggested a wave model. This video looks at these models and the way each model is used to explain key phenomena, as well as examining the outcome of the so called debate. |
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2. Diffraction -Young's Double Slit Experiment and Diffraction Gratings
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Diffraction Grating
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In the early 1800s, Thomas Young decided to set up an experiment to verify the wave nature of light. This became Young's double slit experiment and provided compelling evidence of the wave nature of light. This video examines the basis of this experiment including a mathematical analysis for the behaviour. |
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A brief summary of Young's double slit experiment, useful for review
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Diffraction Grating
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Instead of using one, two or three slits to produce to diffraction and thus interference patterns (thereby demonstrating the way of nature of light), diffraction grating s are in essence many slits, like, well, a grating.
The result is much more defined diffraction patterns which increases the precision of the measurements. This video discusses the physics principles behind the fraction with some examples. |
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This is a simulation of light being diffracted by a double slit, intended for anyone looking to learn about diffraction and interference. By Tom Walsh
The animation lets you explore the effect of grating, wavelength and distance to the maxima separation. By Tom Walsh
3. The nature of Light - its speed determination
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Prior to the 17th century, light was thought to travel instantaneously. However, starting with the work of Rømer, various techniques were developed to demonstrate that light has a finite speed and this the speed could be determined.
These experiments can be roughly divided into two methodologies: astronomical - with the work of Rømer and Bradley and time of flight - , with the work of Fizeau and Foucault In part one, his video discusses the principles behind these four scientists' work. |
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In part 2 of the series, we look at the work of Essen using a microwave cavity to determine the speed of light more accurately We will also examine how you can model the experiment using your own microwave oven. |
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In part 3, I look at more recent efforts in determining the speed of light, leading to the point where the speed was set. I also look at the reason why and its a discussion on how we measure variables with increasing precision.
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4. The nature of Light - Maxwell and electromagnetism
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In the 1830s Michael faraday's work established a relationship between electricity and magnetism however he did not have the mathematical skills to verify mathematically. Enter James Clerk Maxwell. Maxwell sent out to unify the electric and magnetism laws, and in doing so established the new theory of electromagnetism. This culminated in the understanding that light is a form of electromagnetic radiation travelling at a fixed speed.
This video looks at Maxwell's equations in a non mathematical way and how that led to a totally new understanding of the nature of light. |
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5. Spectroscopy
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In the late 1600's Sir Isaac Newton was able to show that white light is made up of a number of colours, due to the dispersion of light through prism. This eventually lead to a deeper understanding of light - that light could be analysed if you could spread it out into its different wavelengths, whether through the dispersion or diffraction, allowed us learn more about the object in emitting that light. This video examine what spectroscopy is, including absorption and emission spectroscopy and includes a demonstration at the University of Sydney. |
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6. Polarisation
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Light is form of electromagnetic radiation, which is a transverse wave. However, the plane at which we receive those transverse waves is not all the same. The three receive many planes of electromagnetic radiation.
Polarisation is the process by where only one plane of electromagnetic radiation is allowed to pass. That's the property of polarisation is evidence of a wave nature of light. This video address is: What is polarisation and how does it demonstrate the wave nature of light? |
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This interactive looks at how polarisation works. By Tom Walsh
7. The Blackbody curve and Wien's Law
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In the latter half of the 19th century scientists studied light coming off heated black bodies, and discovered, when they graft the intensity of each wavelength with the wavelength the graph had a very characteristic shape. This became known as the black body curve. As scientists examined the energy coming off black bodies experimentally, they established some relationships of the curve with temperature. One of these was by Wilhelm Wien who established a relationship between the wavelength with the greatest intensity with the temperature of the emitting body.
This video examines the basics of the blackbody curve and its relation to the temperature of a radiation emitting blackbody, as described by Wien's Displacement Law. |
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Numerous scientists in the late 1800s were interested in the nature of the radiation coming off black bodies and the temperature of those black bodies. Apart from Wien, who is established the Displacement Law (as previously discussed), two other scientists, Stefan and Boltzmann, established a relationship between the total intensity of radiation of a black body with its temperature. This became Stefan-Boltzmanns law.
What was missing at the time was a mathematical basis for the blackbody curve. This eventually led Max Planck to postulate light that the energy of a black body is given off discreetly that is in fixed amounts. This was in contrast to the belief that energy needed to be emitted continuously. Nonetheless his postulate that allowed him to develop a mathematical model to explain the shape of the curve and led eventually to a quantum understanding of nature.
What was missing at the time was a mathematical basis for the blackbody curve. This eventually led Max Planck to postulate light that the energy of a black body is given off discreetly that is in fixed amounts. This was in contrast to the belief that energy needed to be emitted continuously. Nonetheless his postulate that allowed him to develop a mathematical model to explain the shape of the curve and led eventually to a quantum understanding of nature.
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7. Rayleigh Scattering - why the sky is blue
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This video examine the behaviour of Rayleigh scattering in the context why the sky is blue during the day, and why sunrises and sunset are red-orange.
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8. The physics of colour
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