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Reflection and refraction of light Mirrors and lenses. Ch 22: Reflection and refraction. Reflection –part of the light encountering the second medium bounces off that medium.
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Ch 22: Reflection and refraction • Reflection –part of the light encountering the second medium bounces off that medium
Refraction- the light is passing into the second medium bends through an angle with respect to the normal to the boundary
Reflection of light: -specular reflection -diffuse reflection • Normal- a line perpendicular to the surface
v • Refraction sinθf/sinθi=v2/v1=ct • The path of a light ray through a refracting surface is reversible
The Law of Refraction • The index of refraction is a ration n=c/v • n= speed of light in vacuum/ speed of light in a medium • As light travels from one medium to another, its frequency doesn’t change. v= f λ λ1/λ2=v1/v2=(c/n1)/(c/n2)=n2/n1 λ1n1=λ2n2 • Snell’s law of refraction: n1sinθ1=n2sinθ2
Dispersion and Prisms • Dispersion – the dependence of the index of refraction on a wavelength • Snell: the angle of refraction made when light enters a material depends on the wavelength of the light
Total internal reflection occur when light encounters the boundary between a medium with a higher index of refraction and one with a lower index of refraction • Critical angle: θ2=90o n1>n2: sinθc=n2/n1
Ch 23: Mirrors and Lenses • Consider a point source of light (object), after reflection, the rays diverge , but they appear to the viewer to come from a point behind a mirror (image)
Images are formed at the point where rays of light actually intersect or where they appear to originate • p- object distance; • q-image distance; -Real image- light asses through the image point -Virtual image- light doesn’t pass through the image point but appears to come (diverge) from there
The image formed by an object placed in front of a flat mirror is as far behind the mirror as the object is in the front of the mirror • the object height h = the image height h’ • The lateral magnification (def): • M=h’/h =the image height/ the object height
Mirror properties: • The image is as far behind the mirror as the object is in the front • The image is unmagnified, virtual and upright
M=h’/h =-q/p • Mirror equation: • 1/p + 1/q =2/ R • f=R/2 → 1/p +1/q =1/f (q- image distance; p- object distance, R-radius of curvarture)
Convex mirrors (divergin mirrors)
Ray diagrams for mirrors: • 1. Rays 1 is parallel to the principal axis and is reflected back through the focal point • 2. Ray 2 is drawn through the focal point and is reflected parallel to the principal axis • 3. Ray 3 is drawn through the center of curvature, C, and is reflected back on itself
Flat Refracting surfaces: • n1/p=-n2/q • q=- (n2/n1)p • The image formed by a flat refracting surface is on the same side of the surface as the object
M=hi/ho=-q/p • tanθ=AC/f → tan θ=-hi/q-f • ho/f =-hi/q-f → q/p =q-f/f → 1/p +1/q =1/f –thin lenses equation • 1/f=(n-1)(1/R1 – 1/R2) –lens maker’s equation