Lesson Plans

Physics: Principles with Applications 5th Revised Edition ©2002

by Douglas Giancoli

Week 25

Chapter 23: Light: Geometric Optics

College Board Performance Objectives:

• Describe the characteristics of plane mirrors.
• Demonstrate an understanding of the nature of the images formed by plane mirrors.
• Distinguish between virtual and real images.
• Define magnification in terms of image height and object height.
• Distinguish between plane mirrors and spherical mirrors.
• Understand the characteristics of converging and diverging mirrors.
• Describe the images formed by converging and diverging mirrors.
• Use ray-tracing techniques to construct images formed by spherical mirrors.
• Define the focal length of a spherical mirror.
• Use the spherical mirror equation to solve problems.
• Calculate the magnification of a spherical mirror.
• Define index of refraction.
• Understand the relationships between index of refraction, Snell's law, and critical angle.
• Distinguish between converging and diverging lenses.
• Understand the characteristics of converging and diverging lenses.
• Describe the images formed by converging and diverging lenses.
• Use ray-tracing techniques to construct images formed by lenses.
• Define the focal length of a lens.
• Use the thin lens equation to solve problems.
• Calculate the magnification of a thin lens.
• Understand the sign convention for thin lens calculations.
• Apply the lensmaker's equation to solve for unknown parameters related to the construction of lenses.

College Board Lab Objectives:

• Investigate the positions and characteristics of images produced by plane and curved mirrors.
• Observe the positions and characteristics of images produced by convex and concave lenses.
• Design an experiment that would give the magnification of a given lens for a given distance.

Suggested Labs:

• Plane Mirrors
• Concave Mirrors
• Focal Length of a Mirror
• Index of Refraction of Glass
• Index of Refraction using a Microscope
• Focal Length of a Lens

Resources:

• Chapter 23: Light: Geometric Optics — pp. 683–715
• Student Study Guide — pp. 23-1–23-24
• Instructor's Solution Manual — pp. 330–349
• Test Item File — pp. 403–426

Pacing Guide:

• The Ray Model of Light—day 1
• Plane Mirrors—day 1
• Spherical Mirrors—days 1 and 2
• Index of Refraction—day 2
• Snell's Law—day 2
• Thin Lenses; Ray Tracing—days 3 and 4
• The Lens Equation—days 3 and 4
• The Lensmaker's Equation—day4
• Lab—day 5
• Block Scheduling
  The ray model of light, plane mirrors, and spherical mirrors require a single block. Index of refraction, Snell's law, and images formed by thin lenses will take two blocks. Stress ray tracing and sign convention in all blocks. The lensmaker's equation will reinforce student understanding of the focal length of thin lenses.

Key Words:

Critical Thinking Questions:

1. A converging lens has a focal length of 15 cm. Determine the image location for the following object positions: (a) 20 cm, (b) 25 cm, (c) 30 cm, (d) 40 cm, (e) 45 cm, and (f) 50 cm. Plot and interpret graphs of (i) the object position versus image position, and (ii) object position versus the reciprocal of image position.
2. A magnifying glass is held 3.0 cm from an object. What is the focal length of the glass if an image three times the size of the object is produced?
3. What is the focal length of a diverging lens that forms an image one-fifth of the size of the object that is placed 20 cm from the lens?
4. A 45° prism is placed in a liquid with a vertical leg placed perpendicular to an incident ray of light. What is the minimum index of refraction of the material for the total internal reflection to occur if the prism is immersed in (a) water and (b) ethyl alcohol?
5. Go to problem 39 on page 719 in the textbook and show that the displacement distance d can be calculated by:
6. A Lucite block is placed over a dime on your desk. The dime appears to be 2.5 cm below the top of the block. Determine the thickness of the block.

Troubleshooting Tips/Error Traps:

• Students may have trouble with reciprocals in the equation using focal length. Have them use the 1/x (reciprocal) function on their calculator.
• Students may fail to use a negative sign in the working equation for the focal length of a diverging lens or mirror. Examples will help.
• Students may confuse concave lenses with concave mirrors. Examples will help.
• Students may have difficulty in relating focal length, object distance, image distance, and magnification to mirrors and lenses. Have the students make up a table for converging and diverging mirrors and lenses and relate real, virtual, upright, inverted, and sizes of images to object and image distances.

End of Chapter Activity:

Key to choices for multiple choice questions 1 to 7:
I. real
II. virtual
III. upright
IV. inverted
V. smaller than the object
VI. same size as the object
VII. larger than the object

1. The image formed by a plane mirror is
   1. II, III, and VI
   2. I, III, and VI
   3. II, III, and V
   4. I, III, and V
   5. II, III, and VII
2. The image formed by a concave mirror of an object that is located between the focus and the surface of the mirror is
   1. I, III, and VII
   2. I, IV, and V
   3. II, III, and VII
   4. II, IV, and V
   5. I, IV, and VII
3. The image formed by a convex mirror of an object is
   1. I, III, and V
   2. I, IV, and VI
   3. II, III, and V
   4. II, III, and VI
   5. II, IV, and VII
4. The image formed by a concave mirror of an object that is located at the center of curvature of the mirror is
   1. I, III, and V
   2. I, III, and VI
   3. I, III, and VII
   4. II, IV, and V
   5. I, IV, and VI
5. For an object located at a distance beyond twice the focal length of a lens, the image is
   1. I, III, and V
   2. I, IV, and V
   3. II, III, and VI
   4. II, III, and VII
   5. I, IV, and VII
6. For an object located at a distance between one and two focal lengths from a lens, the image is
   1. I, III, and V
   2. II, IV, and V
   3. I, III, and VI
   4. II, III, and VII
   5. I, IV, and VII
7. For an object located between the focal point and a lens, the image is
   1. I, III, and V
   2. II, IV, and V
   3. I, III, and VI
   4. II, III, and VII
   5. I, IV, and VII
8. A beam of light traveling in air is incident on a transparent medium at an angle of 35° with the normal. If the angle of refraction is measured to be 22°, the index of refraction of the medium is
   1. 0.65
   2. 0.92
   3. 1.23
   4. 1.53
   5. 1.65
9. A transparent plastic has an index of refraction of 1.5. The velocity of light in this material is
   1. 1.5 x10⁸ m/s
   2. 2.0 x10⁸ m/s
   3. 2.5 x10⁸ m/s
   4. 2.8 x10⁸ m/s
   5. 3.0 x10⁸ m/s
10. A thin converging lens has a focal point of 30 cm. An object is located 10 cm from the lens. The image distance is
    1. –15 cm
    2. 15 cm
    3. –30 cm
    4. 30 cm
    5. –7.5 cm
    
    

answers: 1 (a), 2 (c), 3 (c), 4 (b), 5 (b), 6 (e), 7 (d), 8 (d), 9 (b), 10 (a)

Suggested Problem Assignments: