Reflection and refraction of light Mirrors and lenses

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: