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reflection & refraction of light

reflection & refraction of light. light. c = f  light: wavelike oscillation of E and B fields (just like any electromagnetic radiation). The only things special about it, is that we can see it. light rays and wave-fronts. isotropic light source (uniform in all directions):

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reflection & refraction of light

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  1. reflection & refraction of light

  2. light • c = f  • light: wavelike oscillation of E and B fields (just like any electromagnetic radiation). The only things special about it, is that we can see it. reflection & refraction of light

  3. light rays and wave-fronts • isotropic light source (uniform in all directions): • the wavefronts indicate maxima in the E/B oscillations • the rays indicate the direction of the wave fronts • I=Psource/(4R2) I: intensity (W/m2) Psource :power of source. R distance from source rays reflection & refraction of light

  4. from now on… • We often only draw the light rays and not the wave-fronts. • But sometimes it is easiest to think in terms of the wave-fronts. reflection & refraction of light

  5. reflection normal • Consider a light ray that strikes a mirror. It will be reflected. • The angle of incidence (relative to the normal to the plane) equals the the angle of reflection • r = i • The mirror must be very flat for this to be true i r mirror reflection & refraction of light

  6. virtual image • If we look at a mirror, we see an image at a location where the object not really is. • The image is formed at a location where there is no light present. • This is called a virtual image. reflection & refraction of light

  7. index of refraction and speed of light • In vacuum, the speed of light equals c = 3x108 m/s. • In any other medium, light propagates more slowly.. • in air: v = c/1.0003 • in water: v = c/1.33 • in glass: v = c/1.5 • in general: v = c/n where n = index of refraction • n also depends on the wavelength () n is larger for smaller  this effect is called dispersion reflection & refraction of light

  8. refraction • if light passes from one medium with refractive index n1 to a medium with refractive index n2 it is bent (refracted): Snell’s law: n1 sin1 = n2 sin2 reflection & refraction of light

  9. refraction II • if nnew > nold then the light ray bends towards the normal when crossing the boundary. • if nnew< nold then the light ray bends away from the normal when crossing the boundary. reflection & refraction of light

  10. demo • consider a light ray traveling from air to water at an incident angle of 300. Given nwater=1.33, what is the angle of refraction? • Now, consider the light-ray traveling from water to air at the same incident angle. What is the angle of refraction? 2=sin-1(n1sin1/n2) =sin-1(1xsin300/1.33)= = 22.080 n1/n2=sin2/sin1 2=sin-1(n1sin1/n2) =sin-1(1.33xsin300/1.)= = 41.60 reflection & refraction of light

  11. at air-glass interface: 2=sin-1(n1sin1/n2)=sin-1(1xsin300/1.5)= 19.470 at glass-air interface 2=sin-1(n1sin1/n2)=sin-1(1.5xsin19.470/1.)= 300 question • a light ray hits a 1 cm glass plate (n=1.5) at an incident angle of 300. The light emerges from the glass plate at an angle • a) <300 • b) =300 • c) >300 =300 =??? http://www.phys.pe.kr/bbs/view.php?id=wave&page=1&sn1=&divpage=1&category=3&sn=off&ss=on&sc=on&select_arrange=headnum&desc=asc&no=11 reflection & refraction of light

  12. question: harpoon fishing • You are standing on the shore near a lake and see a fish in the water which you want to spear. Should you aim the spear a) directly at the fish, b) just above it or c) just under it? answer c) b a c reflection & refraction of light

  13. consider a ray of light traveling from water to air. since nwater > nair a light ray is bent away from the normal If is larger than 1.00, this equation has no solution,  Total Internal Reflection. (There is always some reflection – reflection gets stronger as the critical angle is approached.) total internal reflection nair sin 2 = nwater sin 1 nwater sin1 reflection & refraction of light

  14. when traveling from a medium 1 to a medium 2 with n1>n2: if sinI>n2/n1refraction is not possible and all light will be reflected; =sin-1(n2/n1) is called the critical angle internal reflection II reflection & refraction of light

  15. transport of light! demo reflection & refraction of light

  16. dispersion • The index of refraction depends on the wavelength (I.e. color) of the light. • this can be used to separate white light into its component colors. demo reflection & refraction of light

  17. rainbow • depending on the location of the raindrop and the angle a person is looking at it, only light of a certain wavelength (color) is visible. • The angle (location) changes depending on where the drop is, so that one sees different colors at different locations in the sky… reflection & refraction of light

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