L34_a - REFRACTION The speed of light varies between...

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Unformatted text preview: REFRACTION The speed of light varies between different transparent materials • Result: Light crossing a boundary between materials with different speeds of light at an angle to the normal is BENT SNELL’S LAW: • Relates bending of refracted ray to speed of light in materials constant sin sin 1 2 1 2 = = v v θ θ • When wave crosses boundary, frequency remains constant but wavelength changes o can derive Snell’s law from change in direction of continuous wavefronts when wavelength changes θ 1 θ 1 θ 2 v 1 v 2 normal refracted ray material 2 material 1 reflected ray incident ray SNELL’S LAW from WAVEFRONTS • Look at green and yellow triangles 1 1 2 2 sin sin (common) hypotenuse θ λ θ λ = = • So: 2 1 2 1 2 1 sin sin θ θ λ λ = = v v INDEX OF REFRACTION ( n ) : • define medium in light / v c n = where c is the speed of light in vacuum (or air) o v ≤ c always so n ≥ 1 always ¡ air n ≈ 1 ¡ glass n ≈ 1.5 ¡ water n ≈ 1.33 ¡ diamond n ≈ 2.4 Can now write wavelength in material in terms of n and wavelength in vacuum f v 2 2 = λ f v 1 1 = λ θ 2 θ 1 θ 1 θ 2 SNELL’S LAW AND INDEX OF REFRACTION:...
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L34_a - REFRACTION The speed of light varies between...

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