Download Guided Discovery and Lesson Notes on Mirrors and Applications

Guided Discovery and Lesson Notes on Mirrors and Applications
Objectives: For you to be able to
1. describe the image produced by a plane mirror
2. define the focal point & explain origin of parallel rays
3. explain the rules of ray tracing in concave mirrors
4. define spherical aberration & describe uses of parabolic mirrors
5. explain how concave mirrors form real & virtual images; locate the
image with ray diagrams.
I. The Law of Reflection. Read page 348.
A. In your own words, state the law of reflection. How are the angles of
incidence and reflection specified (wrt what line?)?
B. From what kind of surface is a diffuse reflection produced? Into what
direction(s) does the reflected light travel?
C. From what kind of surface is a regular (also called specular) reflection
produced? How does a regular reflection differ from a diffuse reflection?
II. Objects and Their Images in Plane Mirrors. Read pages 368-369.
A. What is a plane mirror?
B. In optical terms, what is an object? Is it luminous or illuminated?
C. In your own words, define the “image” of an object produced by a plane
mirror? Why is the image produced by a plane mirror described as a “virtual” image?
D. Describe the image of an object produced by a plane mirrors in terms of the
size of the image, its distance from the mirror and its orientation (erect or inverted).
E. What is reversed in the image?
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III. Concave & Parabolic Mirrors. Read pages 370-371. The following notes apply.
A. Concave Mirrors
1. A concave mirror reflects light from its inner surface (“caved in” part).
2. Usually describe spherical mirrors, but sometimes use parabolic ones
3. For spherical mirrors, the mirror is part of the inner surface of a hollow
sphere.
B. Concave Spherical Mirrors
1. Mirror has radius of curvature “r” (radius of the sphere).
2. Line perpendicular to surface that passes through center of mirror (A)
is called the principal axis of the mirror.
.C
F.
A .
3. Point C is the center of curvature of the mirror (all points on the surface
of the mirror are a distance r from this point).
4. The point F is the focal point of the mirror. Any ray traveling close to
& parallel to the principal axis will be reflected through F. F is mid-way between C & A.
5. The focal length, f, of the mirror is the distance between F and A. It is
equal to one-half of the radius of curvature of the spherical mirror.
C. Spherical Aberration & Parabolic Mirrors
1. Parallel rays far from the axis do converge at a point slightly closed to
the mirror than the focal point: thus, the image formed by parallel rays is a disk instead of
a point.
2. This deviation from an ideal point is called spherical aberration.
3. Spherical aberration can be eliminated using parabolic mirrors, which
have many applications, especially where high quality optics/images are concerned. For
example, they are used in flashlights, car headlights, and searchlights.
D. Real Vs Virtual Images
1. If rays actually converge and pass through an image, it is a real image.
A real image can be projected onto a piece of paper or a screen.
2. If the rays actually diverge and only appear to converge, the image is a
virtual image. A virtual image cannot be projected onto a screen or captured on
a piece of paper (because the light rays do not converge at a virtual image).
IV. Images formed by Concave Mirrors
A. Can form both real & virtual images depending on distance object is from
mirror. Locate images using ray tracing and mirror equation.
B. Rules for locating images formed by mirrors using ray tracing.
1. Incident light rays parallel to principal axis are reflected through focal point.
2. Incident rays that pass through focal point are reflected parallel to principal
axis.
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