Ch. 22 Light: Geometric Optics

What does geometric optics state?

• light travels in straight lines

• light bounces back/reflects

When light strikes an object, what can it result in?

• reflection

• absorption

• transmission

Where is theta always measured?

• measured from normal (where it hits object, perpendicular)

What are the 2 types of surfaces light can reflect off of?

Rough

• diffuses reflection = scatters it everywhere

• many angles

Smooth

• specular relfection (clean/mirror)

• only ONE angle

What are the 2 types of images of light?

1. Virtual

   • upright (same as object)

   • NOT projected on screen

   • light does NOT go through

   • distance ««« focal length

2. Real

   • upside down

   • CAN be projected

   • Light goes through

   • distance »»»» focal length

when lookin at spherical mirros, what is one special thing it has?

Radius of Curvature (R)

• part of sphere with certain radius

What is the focal length (f)?

• distance from the mirror to the focal point where light rays are parallel to the axis converge (or appear to converge)

What does it mean for the mirror when the focal length is (+) / (-)?

Concave (f) = (+)

convex (f) = (-)

Explain what a plane mirror is

• flat

• image is the same distance behind the mirror as the object is in front

• VIRTUAL image

Explain what a concave mirror is

• inner surface of the sphere

• focal point on object side of mirror

• f » » » 0

• both REAL + VIRTUAL

Explain what a convex mirror is

• outer surface of sphere

• focal point on opp. side of mirror

• f ««« 0

• ONLY VIRTUAL

How does light reflect for light rays that are parallel and strike a concave mirror?

reflect inward and converge at the focal point

what does it mean for a mirror to have spherical aberration?

• causes blurring

• if radius of curvature is large, mirror behaves like a flat surface and light rays do NOT meet

How is the image location and type found?

• use 2 rays (3 is better)

  • 1 = parallel to axis and reflects at f

  • 2 = passes through focal but paralell to axi

  • 3 = aimed at center curvator (reflects at same path)

If magnification is (-) then the image is …?

inverted

What does it mean if d_o « (f) (object distance from mirror)?

means d_i « 0

• image is behind mirror + virtual

• (+) magnification

• upright

what does it mean if there is a convex mirrors?

• focal point behind mirror

• image behind mirror

• f = (-)

What does index of refraction mean?

• how much light slows down in material

• n always »»»» 1

what does refraction mean?

when light passes between 2 different materials

• due to speed of light being different in the materials

what is total internal reflection?

• when light tries to go from dense to less dense it can reflect inside instead of exiting

when does total internal reflection occur?

• angle is larger than critical angle

• the refracted ray bends at 90

  • angle must be larger to cause total internal reflection

what is a fiber optic cable?

flexible light pipe

• little light loss becuase it refelcts traveling down

What are the 2 kinds of lenses?

• converging (convex)

  • thick center

  • rays bend toward each other

  • REAL or virtual

• diverging (concave)

  • thin in center

  • rays bend away from each other

  • virtual/upright/small

where is the focal point for thin lenses?

• where light rays from a distant source converge

• doesn’t matter if lens is turned around

  • it is the same

what is a focal plane?

plane with all focal points

• light riotates so rays stay parallell

what is the power of a lens?

the ability of the lens to bend light

• focal length is very important

How does it work if you are combining lenses?

• work one lens at a time

• image form 1st lens becomes object for 2nd

• total magnification is product of all individual magnifications