Frontmatter

This book is dedicated to Carl Curtis Duzen, 1937–2020. Carl was an exceptionally accomplished physics teacher. He loved teaching, he loved his students, and he loved physics. With a twinkle in his eye, he would share that he had taught Kobe Bryant about projectile motion. His lessons were always clear, correct, and often wrapped in a bit of humor. To share his experience and knowledge, Carl got us involved in traveling around Pennsylvania doing workshops for fellow teachers as part of the AAPT/PTRA Program. The seed that grew into this book is from the materials developed to support these workshops.

1. CONDITION: During the school year there is a limited time to teach physics; thus, you cannot teach everything in physics. What is (are) the major goal(s) of the precollege or college physics course?

2. QUESTION: What content area is the best to teach? What content area is best suited for teaching the goal(s) of a precollege or college physics course?

3. POSTULATE: Geometric and physical optics.

4. RATIONALE:

   • Almost all geometric optics topics can be illustrated with interesting and engaging demonstrations.

   • Almost all geometric optics topics can be investigated with an easily done inquiry laboratory activity, using readily available materials.

   • Optics is an artistically pleasing topic.

   • Equipment and materials needed are inexpensive, readily available, and relatively student-proof.

   • Geometric optics laboratory activities are not difficult for students to do, and the laboratory activities lead to data students can analyze with convincing results. Opportunities for extra or extended activities on laboratory activities are extensive.

   • Geometric optics gives students a good opportunity to use the mathematical tools from geometry and algebra. Higher levels of mathematics are not needed.

   • Geometric optics provides a good story line illustrating the development of scientific ideas, such as the existence of “proof,” the interaction between theory and experiment, the development of models to represent physical phenomena, how understanding leads to applications, how ideas are connected to each other (i.e., testing consequences of an existing idea), etc.

   • Many of the laboratory activities use graphical analysis of laboratory data acquired by students.

   • Geometric optics permits many students who function at concrete operational level (Piaget) to achieve success.

   • Geometric optics is related to many areas of current research in physics (e.g., photonics, communication, optical fibers, holograms, etc.).

   • Geometric optics topics attract male and female students alike.

   • Geometric optics meets the Next Generation Science Standards.

   • Geometric optics laboratory activities are “doable” and nontrivial.

   • Practical (i.e., engineering) applications are easy to illustrate and understand.

The physicist in each of us wants to explain the natural world we observe. However, before any explanations can be attempted, accurate observations must be made of what we wish to explain. An observation is a record of what your senses tell you about the natural world. Very often, these observations are expressed as measurements. When a measurement is made, a number with a unit is associated with the observation. For example, when someone says “1.2 m”, “1.2” is the number, and “meters” is the unit. The importance of measurement for understanding the natural world is nicely expressed by the following:

Throughout this teacher resource, many activities will involve measurement of optical quantities. The following is a list of typical topics for a unit on geometric optics. Each topic references the appropriate activities in this resource. For some teachers the directions may seem over-prescriptive. The authors felt that if this is the case it would be easier for a teacher to remove some of the directions rather than to add additional directions.

• THE STORY OF BLIND SOCIETY – PROPERTIES OF LIGHT (see Activity 1) Jim Nelson The Physics Teacher, Vol. 24, pg. 346, Sept 1986.

• SOURCES OF LIGHT (see Activity 2)

  • Luminous source vs indirect source of light (post laboratory discussion)

  • Ideal point source vs real extended source of light (post laboratory discussion)

• RECTILINEAR PROPAGATION

  • People pins (demonstration and discussion: see Activity 2)

  • Pinhole camera (see Activity 3)

  • Shadows (see Activity 4)

    1. Sharp shadow – Ray diagrams

    2. Fuzzy shadow – Ray diagrams

    3. Phases of Moon and eclipses (see Activity 5)

  • Inverse square law for illumination (see Activities 6, 7, 8, 9, and 10)

  • Speed of light (see Activity 11)

• PROPERTIES OF IMAGES (discussion)

  • Real vs virtual image

  • Size (magnification = H_i/H_o)

  • Upside down vs right-side up

  • Position

    1. Direct aim

    2. Parallax

    3. Screen test (works for real images only)

• REFLECTION OF LIGHT AND MIRRORS

  • Flat mirrors (fold light) (see Activities 12, 13, 14, and 15)

    1. Angle of incidence = Angle of reflection (∠i = ∠r) (see Activity 14)

    2. Properties of image formed by reflection of light from a flat mirror (see Activities 12, 13, 14, 15, 16, 17, and 18)

       • Virtual image

       • Size: (magnification = 1)

       • Right-side up (pull your nose)

       • Position d_o = d_i

    3. Two-way mirror (window into “image” space)

    4. Retro reflector (see Activity 15)

    5. Kaleidoscope (see Activity 15)

  • Concave (converging) mirrors (see Activities 19, 20, 21, 22, 23, and 24)

    1. Shape of mirror

       • Focal point (F) vs focal length (f)

       • Spherical (R = 2f)

       • Effects of rays far from principle axis (i.e., spectral aberration)

       • Parabolic

    2. Principal rays (see Activity 22)

       • Parallel ray

       • Focal ray

       • Vertex ray

       • Central ray

    3. Properties of image (depends on object's location)

       • Real if object between infinity and F

       • Magnification >1 if object between 2F and V

       • Upside down if object between infinity and F

       • Position given by:

         $1f=1do+1di$

         (3.1)

  • Convex (diverging) mirrors (see Activity 22)

  • Reversibility of light path

    1. Shape of mirror

       • Focal point (F) vs focal length (f)

       • Spherical (R = 2f)

       • Parabolic

    2. Principal rays

       • Parallel ray (virtual focal point)

       • Focal ray (draw away from focal point)

       • Vertex ray

       • Central ray

    3. Properties of image

       • Virtual

       • Magnification <1

       • Right-side up

       • Position given by:

         $1f=1do+1di$

• REFRACTION OF LIGHT AND LENSES

  Refraction makes a nice study of the relationship between theory and evidence. If you start without knowing Snell's law, proceed as follows:

  • I.

    Develop graphs of angle of incidence and refraction from class data.

  • II.

    Show that a parabola will not fit the data.

  • III.

    Do the refraction problem by using graphs to illustrate how much engineering is done when you have no underlying physical law.

  • IV.

    Explore theoretical physical models that reveal an “unexpected” law to test (e.g., the sine law for refraction).

  • V.

    Find a test that will distinguish between possible models (e.g., the speed of light in different materials).

    • Snell's law n₁ sin θ₁ = n₂ sin θ₂ (see Activities 25, 26, 27, 28, and 29)

      1. Index of refraction

         • Relative index of refraction (see Activity 33)

         • Absolute index of refraction

         • Critical angle (see Activities 30 and 31)

         • Total internal reflection (see Activity 29)

      2. Speed of light in various materials (e.g., air, water, glass, etc.)

    • Dispersion (e.g., using a prism) (see Activity 32)

    • Converging lens (Activities 34, 35, 36, and 39)

      1. Shape of lens

         • Focal point (F) vs focal length (f)

         • Lens maker's formula for thin lens:

           $1f=(n−1)[1R1+1R2]$

      2. Principal rays

         • Parallel ray

         • Focal ray

         • Vertex ray

      3. Properties of image (depends on object's location)

         • Real if object between infinity and F

         • Magnification >1 if object between 2F and V

         • Upside down if object between infinity and F

         • Position given by:

           $1f=1do+1di$

    • Diverging lens (see Activities 37, 38, and 39)

      1. Shape of lens

         • Focal point (F) vs focal length (f)

         • Lens maker's formula for thin lens:

           $1f=(n−1)[1R1+1R2]$

      2. Principal rays (same as for Converging lens)

      3. Properties of image

         • Virtual

         • Magnification <1

         • Right-side up

         • Position given by:

           $1f=1do+1di$

    • Fresnel lens

    • When using more than two lenses (or mirrors) the image due to the first lens/mirror can sometimes be treated as the “object” for the next lens/mirror

    • Air lenses under water

  • VII.

    ABSORPTION OF LIGHT (see Activity 44)

    • Colors

    • “Black” vs “White”

    • Beer-Lambert law of absorption (see Activity 44)

  • VIII.

    LIGHT PRESSURE (see Activity 44)