Chapter 18Mirrors &

Lenses

Calculate the angle of total

internal reflection in ignoramium

(n = 4.0)

Mirrors•Smooth surfaces that reflect light

waves

Mirrors•Mirrors have been used for thousands

of years by polishing metal

Mirrors•Mirrors producing sharp

& well defined images were developed by Jean

Foucault in 1857

Mirrors•Jean Foucault developed

a method to coat glass with silver making excellent mirrors

Object•The source of the

spreading light waves being

observed

Image•A reproduction of an

object observed through lenses or

mirrors

Image•When you look into a

mirror, you see an image of yourself

Plane Mirror•Mirrors on smooth flat

surfaces that give regular reflection and

good images

Regular Reflection•All reflect waves are

parallel producing a good image

Diffuse Reflection•Reflect waves from a rough surface bounce in

all directions producing a poor or no image

Objects & Images•Objects & images are represented by arrows as to distinguish the top from the bottom

do di

di = do

hi = ho

object image

hiho

Virtual Image•Light rays focus on a

point behind the mirror

Virtual Image•Virtual images are erect: image & object pointing in the same

direction

Concave Mirrors•Light rays are reflect

from the inner (caved in) surface part of a hollow

sphere

Concave Mirrors•Parallel light rays

converge when reflected off of a concave mirror

Concave Mirrors

Principal axis

CF

F: focal point

C: center of curvature

Focal Point•Point at which parallel

light rays converge (reflecting from a

concave mirror in this case)

Focal Length (f)•The distance between the mirror or lens and

the focal point

Center of Curvature

•The center of the sphere whose inner surface

makes the concave mirror

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

do > C: di < do hi < ho

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

do = C: di = do hi = ho

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

do < C: di > do hi > ho

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

Concave Mirrors

do < f: di = BM hi > ho

Problems with Concave Mirrors:

Draw Ray Diagram & Determine Type of Image

Draw Ray Diagram & Determine Type of Image

Draw Ray Diagram & Determine Type of Image

Draw Ray Diagram & Determine Type of Image

Draw Ray Diagram & Determine Type of Image

Mirror & Lens Formula

1 1 1

f do di

= +

Mirror & Lens Formula

f = focal length

do = object distance

di = image distance

Magnification Formula

hi di

ho do

=

Magnificaton hi

ho

M =

Magnification Formula

M = magnification

ho = object height

hi = image height

Problems

A 5.0 cm object is placed 25.0 cm from

a concave mirror with a focal length of 10.0

cm. Calculate:di, hi, & M

A 250 mm object is placed 25 cm from a

concave mirror whose center of curvature is 250 mm. Calculate:

di, hi, & M

A 15 cm object placed 75 cm from a concave

mirror produces an image 50.0 cm from the

mirror. Calculate:f, hi, & M

A 50.0 mm object is placed 0.25 m from a concave mirror with a

focal length of50.0 cm. Calculate:

di, hi, & M

Convex Mirrors•Light rays are

reflected from the outer surface part of

a sphere

Convex Mirrors•Parallel light rays

diverge when reflected off of a convex mirror

Convex Mirrors

do < f: di = BM hi < ho

Spherical Aberration• The parallel rays reflected

off of the edges of a spherical concave mirror miss the focal point, blurring the image.

Spherical Aberration•This is corrected by

using a parabolic concave mirror

Lenses•Transparent material that allows that light to pass through, but refracts the light rays

Concave Lenses•Caved in lenses where the center is

thinner than the edges

Convex Lenses•Bulging lenses where

the center is thicker than the edges

Concave Lenses•Parallel light rays

diverge when passing through a

concave lens

Convex Lenses•Parallel light rays

converge when passing through a

convex lens

Convex Lenses

Convex Lenses

Concave Lenses

Chromatic Aberration• The parallel rays passing

through a lens are refracted at the edges more so than at the center dispersing the colors

Chromatic Aberration•Corrected through lens

coating or double lens effect

Achromatic Lens• A lens that has been made

so that there is no chromatic aberration

Find the image

Eye Glasses• Concave lenses correct

nearsightedness

• Convex lenses correct farsightedness

Nearsighted•Sees close-up well,

but cannot see distances very well

Farsighted•Sees distances well, but cannot see close-

up very well

A 150 cm object placed 75 cm from a concave

mirror produces an image 250 cm from the

mirror. Draw & Calculate: f, hi, & M

A 250 cm object placed 1.5 m from a convex

lens with a focal length 50.0 cm from the mirror. Calculate:

di, hi, & M

A 350 cm object placed 150 cm from a convex

mirror with a focal length -75 cm from the

mirror. Calculate:di, hi, & M

Draw Ray Diagram & Determine Type of Image

Mirror

Draw Ray Diagram & Determine Type of Image

Draw Ray Diagram & Determine Type of Image

Draw Ray Diagram & Determine Type of Image

Mirror

Draw the Ray Diagram

Draw the Ray Diagram

Convex Lenses