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Physics 1161: Lecture 16, Slide 1
- Today’s lecture will cover Textbook
Sections 26-1 -- 1-
- This material will NOT be on exam II.
Physics 1161: Lecture 16
Introduction to Mirrors
Exam
III
Physics 1161: Lecture 16, Slide 2
Light incident on an object
• Absorption
Everything true for wavelengths << object size
• Reflection (bounces)**
• Refraction (bends)
• Often some of each
Physics 1161: Lecture 16, Slide 3
Reflection
θθθθi θθθθr
Angle of incidence = Angle of reflection
θi = θr
(Angles between light beam and normal)
Physics 1161: Lecture 16, Slide 4
Object Location
- Light rays from sun bounce off object and go in
all directions
We know object’s location by where rays come from.
- Color is because some light is absorbed by object before bouncing off.
Physics 1161: Lecture 16, Slide 5
Flat Mirror
- All you see is what reaches your eyes
- You think object’s location is where rays appear to come from.
θθ θθr θθ θθi
Smooth Mirror
Object Image
All rays originating from peak will appear to come from same point behind mirror!
Physics 1161: Lecture 16, Slide 6
Flat Mirror
(3) Lines appear to intersect a distance d behind mirror. This is the image location.
d
(1) Draw first ray perpendicular to mirror 0 = θi = θr (2) Draw second ray at angle. θi = θr
Light rays don’t really converge
there, so it’s a “______________”
Physics 1161: Lecture 16, Slide 10
Two Mirrors
How many images of money will you see (not
including the actual money)?
Physics 1161: Lecture 16, Slide 11
R
Curved mirrors
A Spherical Mirror: section of a sphere.
C = Center of curvature In front of concave mirror, behind convex mirror.
principal axis
light ray
Concave mirror
R
C
Convex mirror
principal axis
light ray R
C•
Physics 1161: Lecture 16, Slide 12
Preflight 16.
An organic chemistry student accidentally drops a
glass marble into a silver nitrate mirroring solution,
making the outside of the marble reflective.
What kind of mirror is this?
(1) concave
(2) convex
(3) flat
Physics 1161: Lecture 16, Slide 13
Concave Mirror
Principal Axis Focus
Rays parallel to principal axis and near the principal axis (“paraxial rays”) all reflect so they pass through the “Focus” (F).
R
f=R/
The distance from F to the center of the mirror is called the “Focal Length” (f).
f =
R
Rays are bent towards the principal axis.
Physics 1161: Lecture 16, Slide 14
What kind of spherical mirror can be used to start a fire?
concave convex
How far from the paper to be ignited should the mirror be held?
farther than the focal length
closer than the focal length at the focal length
Preflight 16.4, 16.
Physics 1161: Lecture 16, Slide 15
Concave Mirror
F Principal Axis F
Rays traveling through focus before hitting mirror are reflected parallel to Principal Axis.
Rays traveling parallel to Principal Axis before hitting mirror are reflected through focus
