Reflection & Refraction Properties of waves and light.
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Transcript of Reflection & Refraction Properties of waves and light.
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Reflection & Refraction
Properties of waves and light
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Reflection: Light
Light is just like any other wave: Reflection = Bouncing back when
encountering a “non absorbing surface” Ex: waves in a pond, light in a mirror Ray tracing: lines describing the direction of
propagation of the wave. They describe the direction of the wave.
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Ray tracing:
How a mirror works: Light scattered or generated by objects are reflected on a mirror. Understanding how light behaves helps use it better!
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Reflection
The phenomenon called reflection follows specific laws.
Reflection from a perfect surface: “specular reflection”
Angle in = angle out
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Reflection
The law of reflection is always valid! The angle of incidence is always equal to the angle of reflection. This is why “rough” surfaces reflect light in all directions
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Reflection
Amount of reflected light is very dependent on the object’s surface. The surface is also responsible for the color in the objects we see.
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How mirrors work! Images are formed.
An image is the point in space from where all the reflected light appear to come from.
Virtual image: light does not go there
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Plane Mirrors
Image characteristics Virtual image Left-right reversed Upright image Unmagnified image
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Curved mirrors
Also follow the laws of reflection
Practical use: Telescopes, shaving mirrors, wide angle mirrors in hallways etc…
2 types: concave and convex
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Spherical mirrors
R=Radius of curvature
F=focal point; f=focal length
C=center of curvature
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Laws of reflection
Light will always follow the laws of reflection. Even in curved mirrors
Concave Convex
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Concave mirror images
Virtual image? Left-right reversed? Upright image? Unmagnified image?
http://micro.magnet.fsu.edu/primer/java/mirrors/concave.html
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Convex mirror images
Virtual image? Left-right reversed? Upright image? Unmagnified image?
http://micro.magnet.fsu.edu/primer/java/mirrors/convex.html
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Refraction
Refraction (or bending of the light) occurs as light passes from one medium to another with different characteristics
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Bending of light
Light gets bent more when traveling into a “denser” medium
Ex: Glass and water
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Why refraction happens?
Because speed of light changes.
Because light is a wave.
Because its wavelength changes in different medium.
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Laws of refraction
Index of refraction depends on: The medium The wavelength (or color
of the light)
n=c/vSnell’s law:
N1 x sin(1) = N2 x sin(2)
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Why the speed changes?
At the atomic scale...Absorption and re-
emission of of light (photons)
Too many interactions slow down the travel time of light
Vacuum n=1.00000 Air = 1.0003 Diamond=2.42
All other properties of refraction can be derived from this fact!
v=f f=c= vn=c/vn= /
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Demo of refraction
http://wigner.byu.edu/LightRefract/LightRefract.html
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Total internal reflection
There is a critical angle for every boundary
When light hits the boundary at this angle it is no longer refracted, but reflected!
Total internal reflection = principle of optical fibers
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References:
http://micro.magnet.fsu.edu/primer/lightandcolor/index.html http://www.glenbrook.k12.il.us/gbssci/phys/Class/BBoard.html