Reflection and refraction of lightMirrors and lenses
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 reflectionNormal- 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 RefractionThe index of refraction is a ration n=c/vn= speed of light in vacuum/ speed of light
in a mediumAs 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 PrismsDispersion – the dependence of the index
of refraction on a wavelengthSnell: the angle of refraction made when
light enters a material depends on the wavelength of the light
Total internal reflection
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 LensesConsider 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- lightasses through theimage point-Virtual image- lightdoesn’t pass through the image point butappears 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 frontThe image is unmagnified, virtual and
upright
Spherical mirrors:
Concave mirrors
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/qq=- (n2/n1)pThe image formed by a flat refracting
surface is on the same side of the surface as the object
Thin lenses: converging lenses and diverging lenses
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
Combination of thin lenses: