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4.5.2B State and Explain Snell’s Law

4.5.2B State and Explain Snell’s Law • Snell’s Law - the product of the index of refraction and the sine of the incident angle in medium 1 is equal to the product of the index of refraction and the sine of the refracted angle in medium 2; n i sin i = n r sin r Sne ll’s Law

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4.5.2B State and Explain Snell’s Law

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  1. 4.5.2B State and Explain Snell’s Law • Snell’s Law - the product of the index of refraction and the sine of the incident angle in medium 1 is equal to the product of the index of refraction and the sine of the refracted angle in medium 2; ni sin i = nr sin r Snell’s Law http://www.physics.gatech.edu/academics/tutorial/phys2121/Java%20Applets/ntnujava/propagation/propagation.html Example 1: A ray of light passes into a rectangular block of crown glass at an angle of 42.0o (measured from normal). What is the angle of refraction inside the block? (show solution in NB) Given: Unknown: Equation:

  2. Example 2: A ray of light in water strikes the boundary between water and air at an angle of 42.0o (measured from normal). At what angle from the normal (ie., angle of refraction) will the light ray emerge from the water air boundary? (show solution in NB) Given: Unknown: Equation:

  3. • Total Internal Reflection (TIR) - a ray of light traveling in a material with a higher n strikes the boundary with a material of lower n and does not leave the original material but is reflected back into the original material;

  4. TIR http://www.physics.uoguelph.ca/applets/Intro_physics/kisalev/java/totintrefl/index.html Before TIR can occur, angle i must excede the critical angle...the angle of incidence which produces angle r = 90.0o.

  5. Example 3: What is the critical angle for the water-to-air boundary? (show solution in NB) Given: Unknown: Equation: In Example 3, when angle i > 48.6o, Total Internal Reflection (TIR) takes place and the ray of light does not leave the original material but is reflected back into the original material such that angle r = angle i (Law of Specular Reflection)...no refraction takes place; SNELL’S LAW a la MACARENA http://www.haverford.edu/physics-astro/songs/macsnell_music.htm 3-D Waves http://id.mind.net/~zona/mstm/physics/waves/wave3d1/wave3d1.htm Reflection, Refraction, Diffraction http://www.lon-capa.org/~mmp/kap13/cd372.htm

  6. 4.5.3 Wave Diffraction • Diffraction- the process by which waves (water, sound, light) bend around obstacles; Diffraction http://hyperphysics.phy-astr.gsu.edu/hbase/sound/diffrac.html Ifl >>> than the obstacle, waves bend around and fill in behind the obstacle as if it wasn’t there... almost no “shadow” region behind obstacle; If l <<< than the obstacle, waves bend around but only fill in a little behind the obstacle... significant “shadow” region behind the obstacle. Diffraction of Water Waves http://www.ngsir.netfirms.com/englishhtm/Diffraction.htm • Why does diffraction occur? Christian Huygens (Dutch, 1600’s, a contemporary of Newton) proposed that every point on a wave front can be considered as the source of a circular wave with the wave front itself being the sum of an infinite number of these wave sources. Thus, when a wave passes an obstacle or through a slit, the side(s) of the wave are cut off and the end point(s) generate circular waves which fill in behind the obstacle/slit.

  7. 4.5.4 Examples of Diffraction • Sound waves bend around corners and through doors; • Water waves diffract around obstacles and after passing through “slits;” • Light shows diffraction patterns after passing through single slits;

  8. 4.5.5 Superposition - Constructive and Destructive Interference •Superposition - the process by which wave amplitudes add together, algebraically (ie., crests [or compressions] act as positive amplitude and troughs [or rarefactions] act as negative amplitude); • When crests add together, the amplitude of the resultant wave increases (constructive interference); • When a crest adds with a trough, the amplitude of the resultant wave decreases (destructive interference); • When troughs add, the negative amplitude of the resultant wave increases (constructive interference). 4.5.6 and 4.5.7 Superposition - the resultant of 2 waves (Leave 1 page blank for several diagrams) Constructive Interference http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave2.html Destructive Interference http://www2.biglobe.ne.jp/~norimari/science/JavaEd/e-wave3.html

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