Download Reflection and refraction of light Mirrors and lenses

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
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
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
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/q
q=- (n2/n1)p
The 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: