Ch22 - Chapter 22 PHY213 A Brief History of Light Chapter...

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Chapter 22 PHY213 1 Chapter 22 Reflection and Refraction of Light Read Ch. 22 (exclude 22.5-6), Ch. 23 (in 23.4, only flat refracting surfaces; in 23.6, no combination lenses) A Brief History of Light s 1000 AD s It was proposed that light consisted of tiny particles s Newton s Used this particle model to explain reflection and refraction s Huygens s 1678 s Explained many properties of light by proposing light was wave-like s Young s 1801 s Strong support for wave theory by showing interference A Brief History of Light, cont s Maxwell s 1865 s Electromagnetic waves travel at the speed of light s Planck s EM radiation is quantized s Implies particles s Explained light spectrum emitted by hot objects s Einstein s Particle nature of light s Explained the photoelectric effect The Particle Nature of Light s “Particles” of light are called photons s Each photon has a particular energy associated with the wave frequency, ƒ s E = hƒ s h is Planck’s constant s h = 6.63 x 10 -34 J·s = 4.135 x 10 -15 eV·s s Encompasses both natures of light s Light travels, with a given frequency, like a wave s Light interacts, with a given point-like bundle of energy, like a particle
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Chapter 22 PHY213 2 Dual Nature of Light s Experiments can be devised that will display either the wave nature or the particle nature of light s In some experiments light acts as a wave and in others it acts as a particle s Nature prevents testing both qualities at the same time Geometric Optics – Using a Ray Approximation s Light travels in a straight-line path in a homogeneous medium until it encounters a boundary between two different media s The ray approximation is used to represent beams of light s A ray of light is an imaginary line drawn along the direction of travel of the light beams Ray Approximation s A wave front is a surface passing through points of a wave that have the same phase and amplitude s The rays, corresponding to the direction of the wave motion, are perpendicular to the wave fronts Reflection of Light s A ray of light, the incident ray
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Ch22 - Chapter 22 PHY213 A Brief History of Light Chapter...

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