Lesson Plans

Physics: Principles with Applications 5th Revised Edition ©2002

by Douglas Giancoli

Week 27

Chapter 25: Optical Instruments

College Board Performance Objectives:

• Describe and compare the optics of the camera and the human eye.
• Discuss some common visual defects and explain how they may be corrected.
• Distinguish between refractive and reflecting telescopes.
• Discuss the advantages to refractive and reflecting telescopes.
• Distinguish between lateral and angular magnification in the microscope.
• Describe the simple and the compound microscope and their magnifications.
• Explain with diagrams the operation of a simple and compound microscope, a refractive and reflective telescope, a camera, and a projector.
• Determine the focal length of a lens system.
• Predict mathematically the nature, size, and location of images formed by optical systems.
• Discuss the significance of resolving power.

College Board Lab Objectives:

• Design an experiment to study the magnification of a simple and a compound microscope.
• Design an experiment to make and use a simple refracting telescope under laboratory conditions.

Suggested Labs:

• Simple Magnifier
• Lens Magnification
• Compound Microscope
• Refracting Telescope

Resources:

• Chapter 25: Optical Instruments — pp. 757–787
• Student Study Guide — pp. 25-1–25-18
• Instructor's Solution Manual — pp. 367–379
• Test Items File — pp. 449–460

Pacing Guide:

• The Camera—day 1
• The Human Eye—day 1
• The Magnifying Glass—day 2
• Telescopes—day 2
• Compound Microscope—days 2 and 3
• Aberration of Lenses and Mirrors—day 3
• Limits of Resolution—day 3
• X-Rays and X-Ray Diffraction—day 4
• Lab—day 5
• Block Scheduling
  The camera and the human eye need a block of time. The magnifying glass, the telescope, and the compound microscope require a block. Aberration, resolution, and x-ray diffraction require a block. Emphasize ray tracing in the telescope and microscope.

Key Words:

Critical Thinking Questions:

1. A converging lens with a focal length of 20 cm is placed 20 cm in front of a diverging lens with a focal length of –10 cm. Where is the final image if an object is placed 30 cm in front of the converging lens? Analyze the problem both mathematically and by drawing ray diagrams.
2. An object is 40 cm in front of a diverging lens of focal length 15 cm. A second converging lens, focal length 10 cm, is 30 cm behind the first lens. Where is the final image? What is its magnification? Analyze the problem both mathematically and by drawing ray diagrams.
3. A pin hole camera with 35 mm film is used to take a picture of a building 8 m high. The film is 120 mm from the pinhole. How far from the building should the camera be held in order to include the entire height of the building?
4. An astronomical telescope has an objective lens of focal length 180 cm and an eyepiece (ocular lens) of focal length 10 cm. Research and prove that the distance between the two lenses is given by: f₀ + f_e = 190 cm
5. A microscope with a tube length of 18 cm is designed to have a magnification of 1000X. If the objective lens has a focal length of 5 mm, what is the focal length of the eyepiece?

Troubleshooting Tips/Error Traps:

• Reinforce with microscope and telescope lens combination examples.
• In problems that utilize two lenses, ray tracing will help students in determining the type and the position of the image to be used as the object for the second lens.
• Stress that color vision is psychological. Vision happens in the occipital regions of the brain.

End of Chapter Activity:

1. What is the f-stop of a camera with a focal length of 3.2 cm and an aperture-opening radius of 2.0 mm?
   1. 0.64
   2. 0.80
   3. 1.00
   4. 1.28
   5. 8.00
2. A converging lens will be prescribed to correct the vision with which of the following vision problems?
   1. nearsightedness
   2. farsightedness
   3. astigmatism
   4. myopia
   5. glaucoma
3. A compound microscope has an objective focal length of 3.00 mm and an eyepiece focal length of 36.0 mm. What is the approximate magnification when the lenses are separated by 20.0 cm?
   1. 14X
   2. 22X
   3. 68X
   4. 220X
   5. 460X
4. By what factor will tripling the focal length of the objective lens change the magnification of a compound microscope?
   1. 1/81
   2. 1/9
   3. 1/3
   4. 3
   5. 9
5. A simple magnifier uses
   1. a converging lens to form a real image
   2. a converging lens to form a virtual image
   3. an objective lens to form a real image
   4. a diverging lens to form a real image
   5. a diverging lens to form a virtual image
6. The focal length of a refracting telescope has a focal length of 100 cm and the eyepiece has a focal length of 50 mm. What is the magnification of the objective-eyepiece combination when the telescope is focused to infinity to view a distant object?
   1. 2X
   2. 20X
   3. 50X
   4. 500X
   5. 2000X
7. A gemstone being examined under a jeweler's loupe appears 7 times larger. If the near point of the observer is 350 mm, what is the focal length of the loupe?
   1. 35 mm
   2. 45 mm
   3. 50 mm
   4. 55 mm
   5. 70 mm
   
   Questions 8 to 10. An object 4.0 cm in height is placed 30 cm in front of a lens with a focal length of 100 mm. A second lens with a focal length of 50 mm is placed 25 cm behind the first lens.
8. The image formed by the first lens is
   1. real and upright
   2. real and inverted
   3. virtual and upright
   4. virtual and inverted
   5. no image is formed
9. In reference to the first lens, the image formed by the first lens is located at an image distance of
   1. 9 cm
   2. 10 cm
   3. 12 cm
   4. 15 cm
   5. 18 cm
10. The image formed by the second lens is
    1. real and upright
    2. real and inverted
    3. virtual and upright
    4. virtual and inverted
    5. no image is formed
    
    

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

Suggested Problem Assignments: