by Brian Skrobot
PHY 301
Fall 1998
Instructor: C. Wenning
UNIT OVERVIEW
A. For this unit, the students will be studying the nature of light. This unit will use a combination of historical and conceptual theories. The students are at the high school level and should have had not only algebra but possibly geometry/pre-calculus as well. This unit plan assumes that the students have already covered wave theory, especially propagation, reflection, refraction, interference, and diffraction. Most of the information from this unit will be taken from the text Modern Physics, copyright 1992, published by Holt, Rinehart, and Winston, Inc. Calculators are recommended.
During this unit, students will not only cover the basic characteristics of light, but will also cover some of the more advanced concepts. Students will be exposed to the historical aspects of light theory, speed of light, the electromagnetic spectrum (focussing on the visible spectrum itself), and lightwaves.
The study of light is important because it links the concept of waves and wave theory to the study of optics.
The information in this unit will show how the concept of wave theory is linked to the concept of optics. It will give the student insight into how the basic theories of light and optics work, from how the human eye perceives images to how we are able to see the light of distant stars.
Society depends on the concept of light for many reasons. These may be as mundane as lighting a busy interstate thoroughfare all the way up to microsurgical techniques. Light may also be focussed as a LASER to bombard deuterium-filled glass spheres to initiate atomic fusion.
3. Scientists depend on light in many ways. They require light to receive images from distant stars. They use light to determine the distance of the moon to within several meters. They also use light to read the values displayed on the very instruments they depend upon.
CONTENT/PROCEDURES OUTLINE
DEFINITIONS
Candela- the unit of luminous intensity of a light source
2. Corpuscular theory- Newtonís theory that light was made up of tiny particles, which he called ìcorpusclesî
3. Electromagnetic spectrum- consists of a tremendous amount of radiation frequencies extending from about 10 Hz to more than 1025 Hz
4. Electromagnetic wave- A periodic disturbance involving electric and magnetic forces
5. First law of photoelectric emission- the rate of emission of photoelectrons is directly proportional to the intensity of the incident light
6. Huygenís principle- each point on a wave front may be regarded as a new source of disturbance
7. Illuminance- the luminous flux per unit area of a surface
8. Illuminated object- an object that is seen because of the light scattered from it
9. Laser- (acronym) Light Amplification by Stimulated Emission of Radiation
10. Lumen- The unit of luminous flux; the luminous flux on a unit surface all points of which are at unit distance from a point source of one candela
11. Luminous flux- the part of the total energy radiated per unit of time from a luminous source that is capable of producing the sensation of sight.
12. Penumbra- The partially illuminated part of a shadow
13. Photoelectric effect- The emission of electrons by a substance when illuminated by electromagnetic radiation of sufficiently short wavelength
14. Photoelectron- Electrons emitted from a light-sensitive material when it is illuminated with light of sufficiently short wavelength
15. Photometer- an instrument used for comparing the intensity of a light source with that of a standard source
16. Photometry- the quantitative measurement of visible radiation from light sources
17. Photon- A quantum of light energy; the carrier of the electromagnetic interaction
18. Planckís constant- A fundamental constant in nature that determines what values are allowed for physical quantities in quantum mechanics; h = 6.63 x 10-34 J ( s
19. Quantum theory- assumes that the transfer of energy between light radiation and matter occurs in discrete units called quanta, the magnitude of which depends on the frequency of the radiation
20. Radiant energy- transported in photons that are guided along their path by electromagnetic waves
Second law of photoelectric emission- the kinetic energy of photoelectrons is independent of the intensity of the incident light
22. Third law of photoelectric emission- within the region of effective frequencies, the maximum kinetic energy of photoelectrons varies directly with the difference between the frequency of the incident light and the cutoff frequency
23. Umbra- the part of the shadow from which all light rays are excluded
24. Visible spectrum- includes the visible light regions as well as the near infrared and the near ultraviolet
UNIT CONCEPT OUTLINE
Properties of Light
Propagation
Reflection
Refraction
Interference
Diffraction
The Corpuscular Theory
Rectilinear Propagation
Reflection
Refraction
The Wave Theory
Huygensí Principle
The Wave Front
Interference of Light
HISTORY: Abandonment of the Corpuscular Theory
The Electromagnetic Theory
HISTORY: Michael Faraday
HISTORY: Tubes of Force (Faraday)
HISTORY: James Clerk Maxwell
Electromagnetic Wave
HISTORY: Heinrich Rudolf Hertz
The Electromagnetic Spectrum
Frequency Range (10 Hz to 1025 Hz)
Velocity of Radiations (3 x 108 m/s)
Spectrum Range (3 x 107 to 3 x 10-7 ()
Radio Wave Region
Power Region
Visible Spectrum (7600 ( to 4000 ()
d. Light (defined)
The Photoelectric Effect
HISTORY: Philip Lenard
Photoelectrons
Laws of Photoelectric Emission
First Law of Photoelectric Emission
Second Law of Photoelectric Emission
HISTORY: Robert A. Millikan
HISTORY: Hughes and Compton
c. Third Law of Photoelectric Emission
Failures of the Wave Theory
The Quantum Theory
HISTORY: Max Planck
Planckís Constant (h = 6.63 x 10-34 J(s)
E = hf
HISTORY: Albert Einstein
Einsteinís Photoelectric Equation
mv2max = hf ñ w
hfco = w
Radiant Energy
The Quantized Atom
HISTORY: Niels Bohr
HISTORY: Ernest Rutherford
Bright Line Spectra
Coherent Light: The Laser
Coherent Light
Amplification
Production of X Rays
Photoelectric Effect
mv2 = hfmax ñ w (Inverse Photoelectric Effect)
Penetrating Properties
The Pressure of Light
HISTORY: Nichols, Hull, and Lebedev
Pressure of Sunlight on Earth (4 x 10-11 standard atm.)
MAJOR OBJECTIVES
A. Upon completion of this unit, the student will be able to:
During this unit, the student will learn the following skills:
Hopefully after completing the course, the students will meet the following scientific dispositions:
ALTERNATIVE CONCEPTIONS
Light illuminates objects, thereby allowing us to see them (INCORRECT).
Eyes ìgrabî images (INCORRECT).
Light does not travel in all directions, but just between the object being illuminated and the eye (INCORRECT).
CLASSROOM METHODS
In Modern Physics, Chapter 12 deals with The Nature of Light. However, I also borrow heavily from Chapter 13: Reflection, Chapter 14: Refraction, and Chapter 15: Diffraction and Polarization.
Lesson Plans:
Mirrors and Lenses (attached)
Objectives- The student will witness that straight, concave, and convex mirrors affect rays of light. They will also observe that lenses of different shapes and thicknesses have varying effects on the light rays.
Content-
1. Convex lenses and concave mirrors both have the effect of causing light rays to converge.
Concave mirrors cause convergence after reflecting the light rays. Convex mirrors allow light rays to pass through and converge.
Concave lenses and convex mirrors both cause divergence of light rays. Convex mirrors reflect the rays and cause them to diverge, while concave mirrors allow the light to pass through before diverging.
DEMONSTRATIONS
Photoelectric Effect
The purpose of this demonstration is to familiarize students with the concept of the photoelectric effect. This will also be the studentís first exposure to the electroscope.
The procedures will be as follows:
Show how the electroscope works by charging it with a rubber rod that has been rubbed on a piece of wool. Discharge the electroscope by grounding it out with a zinc plate.
Charge the electroscope with the rubber rod. Turn on an incandescent light and move it closer to the zinc plate attached to the electroscope. Have the students note that the leaves of the scope do not collapse.
Turn off the incandescent light and turn on a black light. Move the black light so it shines on the zinc plate. The students will see that this causes the leaves of the scope to discharge and collapse.
Trinklein, Frederick E. (1992) Modern Physics. Orlando, Florida.
Holt, Rinehart, and Winston, Inc. (p. 280D)
Shadow Formation
This demonstration is intended to familiarize with the fact that light travels in straight line and how illumination works. This will also introduce the concepts of the umbra and penumbra.
2. The procedures will be as follows:
Place two lamps about 1 meter from a projection screen and adjust them so that they will both shine on the screen.
Using your hand to cast shadows on the screen, having the students notice how sharp the umbra is with your hand close to the screen.
Move your hand towards the lamp. Students will note an increase in the size of the umbra and will now be able to see the penumbra.
Repeat this with the second lamp.
3. Trinklein, Frederick E. (1992) Modern Physics. Orlando, Florida.
Holt, Rinehart, and Winston, Inc. (p. 280E)
Light Travels in Straight Lines
This demonstration links the fact that light travels in straight lines (from the shadow demonstration) to the fact that light rays can normally not be seen.
The procedure will be as follows:
Direct a laser beam across the room. CAUTION: STUDENTS MUST NOT LOOK DIRECTLY INTO THE BEAM!
Place an index card in the path of the beam and slowly walk across the room, keeping the card in the path of the beam. The students will recognize that the beam is traveling in a straight line.
Stand beside the beam and clap two chalkboard erasers together. The dust from the erasers will make the beam visible. Keep clapping the erasers together as you walk along the beam until the entire beam is visible.
3. Trinklein, Frederick E. (1992) Modern Physics. Orlando, Florida.
Holt, Rinehart, and Winston, Inc. (p. 315C)
Reflection
This demonstration will show students that in order for us to see an object, light must first reflect off of that object.
The procedure will be as follows:
Direct a laser beam across the room. CAUTION: STUDENTS MUST NOT LOOK DIRECTLY INTO THE BEAM!
Tape an index card to one wall in the classroom. Direct the beam of the laser onto the card from across the room. Explain that the laser strikes the card as a coherent beam, but the card is a diffuse reflector that scatters the beam as soon as it strikes. A small part of the reflected radiation goes to each part of the room, allowing the laser spot to be seen from any spot in the room.
Tape a plane mirror over the card to deflect the beam. Explain that one beam of light strikes the mirror and one is reflected, with the angle of incidence equaling the angle of reflection. Tap two chalkboard erasers in front of the beams to make them visible.
3. Trinklein, Frederick E. (1992) Modern Physics. Orlando, Florida.
Holt, Rinehart, and Winston, Inc. (p. 315C)
Plane mirror images
This demonstration will show students how light can reflect and form images.
The procedure will be as follows:
Thoroughly clean a sheet of plate glass.
Arrange two candles and the sheet of glass in front of the chalkboard, one candle about 30 cm in front of the glass and the other about 30 cm behind the glass.
Light the front candle. Adjust the rear candle so that reflected flame image appears over its wick (the back candle will appear to be lit).
3. Trinklein, Frederick E. (1992) Modern Physics. Orlando, Florida.
Holt, Rinehart, and Winston, Inc. (p. 315D)
LABORATORY ACTIVITIES
Photometry
Objective- After completing the experiment, the student will know how to measure the intensity of light and how to determine the efficiency of light sources.
Type- Directed
Apparatus-
Meterstick and supports
Photometer (Bunsen, Joly, or photoelectric)
Galvanometer and hook-up wire
Lamp sockets, cords, and plug
Calibrated 40 Watt lamp or new 40 Watt lamp
25 Watt, 40 Watt, 60 Watt, and 75 Watt lamps
Procedure- See attached lab sheet
5. Trinklein, Frederick E. (1992). Modern Physics: Exercises and Laboratory Experiments. Orlando, Florida. Holt, Rinehart, and Winston, Inc.
Plane Mirrors
Objective- After completing this experiment, you should understand the laws of reflection and be able to interpret image formation by plane mirrors in terms of these laws.
Type- Directed
Apparatus-
Plane glass mirror, 6 inches by 1 inches or larger
Rectangular wooden block
Metric ruler
Protractor
Pins
Drawing computer
Rubber bands or cellulose tape
Procedure- See attached lab sheet
5. Trinklein, Frederick E. (1992). Modern Physics: Exercises and Laboratory Experiments. Orlando, Florida. Holt, Rinehart, and Winston, Inc.
Mirrors and Lenses
Objective- After completing this experiment, you should understand the basic laws of reflection of mirrors and convergence/divergence of light by lenses.
Type- Nondirected
Apparatus-
Ray box
Convex lens
Concave lens
Combination mirror (straight, concave, and convex sides)
Protractor
Procedure- See attached lab sheet
Skrobot, Brian (1998)
SAFETY CONSIDERATIONS
Safety Responsibilities
1. It is the responsibility of the school principle to make sure that the school is in compliance with local and state safety regulations including, but not limited to, proper functioning and maintenance of all fire suppression equipment. If the Department Chair or classroom teacher reports a problem with such equipment, then the principle should make corrections to that problem immediately.
It is the responsibility of the Science Department chair to make sure that the classroom teacher is following safe operating procedures in the classroom. The Science Department Chair should conduct periodic inspections of all lab areas to insure that all equipment is in working order and all hazardous materials are secured.
3. It is the responsibility of the science teacher to maintain a safe and organized lab environment. Restricted lab material should be secured in locked cabinets, and all lab equipment must be maintained in proper working order. It is the responsibility of the classroom teacher to ensure that ALL safety procedures are obeyed and followed during lab activities. It is also the responsibility of the teacher to note the locations of and explain the use of all safety equipment in the classroom.
B. Optics is not by itself an inherently dangerous unit. However, part of the optics unit includes the use of 5 mW lasers. These lasers, while low powered, pose a danger of retinal damage is misused. Students will be properly versed in how to use the lasers in the lab and that dangers associated with them. Any student intentionally using the lasers in an incorrect or unsafe manner will be excused from the lab with the proper penalties.
SPECIAL STUDENT NEEDS
A. Several students may come to the classroom with hearing impairments. Hearing impairment involves special problems that must be dealt with.
Specific problems with hearing impairments:
A hearing impaired student may have a problem with obtaining information in the classroom. In general, physics concepts require the student to have access to all of the information given in class. By having a hearing impairment, it is very easy for a student to miss part or all of a new concept, thereby causing a knowledge base to be compromised.
It is possible that a student with a handicap (not specifically hearing impairment) will have difficulties with other students in the class. While not an entertaining subject, students with disabilities are often the targets of other studentsí humor. While we would like to think of physics students as being advanced enough to not partake in such degradation of another student, it does happen.
Accommodations would be as follows:
Always face the class while speaking.
Minimize classroom noise.
Speak in simple, direct language.
Avoid digression or sudden change in topic.
Periodically summarize student input.
Use visual media
If a student is completely deaf, consider a sign language interpreter.
If an interpreter is used, always look at the student when asking questions, not the interpreter.
D. For an enrichment activity, the student may consider written reports or essays. Research papers give a student an opportunity to use a variety of up-to-date sources, including references, newspapers, and scientific magazines or journals.
E. Students with limited English proficiency (LEP) pose special difficulties for the classroom teacher, especially in a class that has a specialized vocabulary (such as Science classes). Students who do not speak English as their first language must have their reading and speaking levels assessed so that instructional methods can be adequately adjusted.
Provide the LEP student with a list of important words for the unit before you discuss them in class.
Allow the student to work with a partner or small group. The LEP student will benefit personally from the experience, and the other students in the group will have the information reinforced by helping teach it to another student. This will also help the other students learn to overcome language barriers.
Speak slowly, restate phrases, and repeat key words.
Use illustrations, pictures, and diagrams as often as possible.
Use videotapes and films to clarify concepts.
Provide the opportunity for oral/visual responses to exam questions.
STUDENT ASSESSMENT
A. Process skills are the meat and potatoes of physics, since hands-on learning tends to remain in the memory for a longer period of time than simple rote memory. One possible assessment would be the use of an optics bench with lenses to recreate an image of an object. Students would be able to visualize the paths of the light rays and the focal point(s) of the images. By using these techniques, the student could also build a crude telescope given the appropriate materials.
B. For the disposition assessment, I would have to use modern imaging devices as a basis. With their knowledge of optics, students could look at modern imaging devices (specifically, the telescopes used by observatories and the Hubble telescope) and based on a cost/effectiveness ratio, determine whether the devices are worth the money spent on them.
C. Rote memory learners will be content with the information given to them in class, even though that is not the type of learning I encourage. Tactile learners will be more inclined to involve themselves in the lab activities, building telescopes and such. Deep learners will (if given the opportunity) divulge large amounts of information on any subject. If deep learners understand optics, you can expect detailed information on any question that you ask. A multiple choice or fill in the blank test could be given, with an essay for the deep learner and possibly a diagram/lab practical for the tactile learner.
CONGRUENCE WITH STATE AND NATIONAL GOALS
The study of optics will expose students to several of the objectives outlined in the Illinois State Goals. Basic vocabulary of optics will be emphasized, as well as the concepts of diffraction, refraction, focal point, and virtual images. Hands-on study will be emphasized with the students using lenses, mirrors, ray boxes, and optics benches. Discussions in this area will include (but not be limited to) the Hubble telescope and other orbital and suborbital observatories. Analysis and graphics will be covered in this unit to reinforce skills that have been learned in previous units of the year. ìNewî technologies such as lasers and fiberoptics will be covered as well.
B. To satisfy national goals, inquiry learning will be given the forefront in this unit. Hands-on work will be the basis for learning about light and optics. Learning will be primarily student-based and will also teach the students several skills in the use of optics.
C. A direct quote from Project 2061ís goals states ìuse models to explain a vast and diverse array of natural phenomenaî. This unit will help facilitate that goal because it is the gateway to the study of high-energy physics, which include energy, force, matter, and quantum physics. By understanding how the universe functions, students gain an insight into how the universe moves around them.
PHILOSOPHY OF TEACHING STATEMENT
Students have the ultimate right to receive a quality education.
Teachers will never be ìperfectî. We must always strive to learn new technologies and curricula. We must always be open to new ideas. The day that we fail to learn something new is the day that we begin to become obsolete.
Human beings must be educated to make the decisions of everyday life. By failing to educate them, teachers have failed to adequately prepare them for the decisions they must make on a day to day basis.
By educating students, we teach them how to grow and achieve in their mental capabilities and attitudes.
Knowledge must be cross-curricular. High expectations must be made of grammatical, historical, and mathematical skills in the science setting.
The primary reason for teaching is the student. We must endeavor to make every day a learning experience. If you teach to gain a paycheck, youíre expendable. If you teach to hear a student say, ìI didnít know that!î, youíre educating.
Education must be relevant. Filling a studentís mind with extraneous material is inexcusable. Life is not an episode of ìJeopardyî.
REFERENCES
Baggott, Jim. (1992) The Meaning of Quantum Theory. Oxford, England.
Oxford University Press.
Edge, R. D. (1987) String & Sticky Tape Experiments. College Park, Maryland.
American Association of Physics Teachers.
Serway, Raymond A. (1995) College Physics, 4th Ed. Orlando, Florida.
Harcourt Brace and Company
Stollberg, Robert (1975) Physics: Fundamentals and Frontiers (Revised Edition)
Boston, Massachusetts. Houghton Mifflin Company.
Trinklein, Frederick E.(1992) Modern Physics. Orlando, Florida.
Holt, Rinehart, and Winston, Inc.
Trinklein, Frederick E. (1992). Modern Physics: Exercises and Laboratory
Experiments. Orlando, Florida. Holt, Rinehart, and Winston, Inc.
Trowbridge, Leslie W. and Rodger W. Bybee. (1996) Teaching Secondary School
Science. Englewood Cliffs, New Jersey. Prentice-Hall, Inc.
MIRRORS AND LENSES
During this activity, you will be using several different shapes of mirrors and lenses to change the direction of beams of light. After completing this experiment, you should understand the basic laws of reflection of mirrors and convergence/divergence of light by lenses.
Place one of the light boxes on the table in front of you. Be careful not to touch the top of the light box during the exercise, as it does tend to get rather hot. Turn on the light box and make sure that the three rays of light are white, not red, blue, and green. This can be adjusted by sliding a color filter over the slots in the front of the box. Place a piece of white paper (provided) in front of the openings to make the rays of light more visible.
Are the lines of light parallel?
If not, how do they differ?
Place a half-convex lens in front of the light source with the flat side against the box. The light rays should now all be going in the same direction.
3. Take the silver mirror and place it in front of the light rays so the straight side of the mirror is reflecting them. Rotate the mirror slightly. What happens to the light rays? Are they still parallel to each other or not?
Use a protractor to measure the angle of both the original and reflected light rays.
What do you notice about the two angles?
Turn the mirror so that the concave side is reflecting the light (The concave side is the one where it looks like someone took a scoop out of it). What happens to the paths of the rays? Turn the mirror back and forth slowly.
Do the paths intersect?
If so, how far from the mirror do they? Is this distance constant no matter where you turn the mirror?
Turn the mirror so the convex side is facing the light. Turn the mirror slowly back and forth. Do the light rays ever intersect?
Why do you think the light acts differently when reflected by a concave or convex mirror as compared to a flat mirror? (If youíre confused, try looking back at some of the previous questions)
Remove the mirror from the table surface and replace it with the concave lens (this is the one that looks like an hourglass). What happens to the paths of the light?
Do they intersect? If so, how far away from the lens?
Replace the concave lens with the convex lens. What happens to the light paths?
Do they intersect? If so, how far away from the lens?
On the sheet of paper youíve been using to make the light easier to see, sketch the paths of the light rays and the position of the lens. Mark the point where the light intersects as focal point A. The focal point is the point at which light rays intersect.
Now place the concave lens between focal point A and the convex lens. What changes? Do the light rays still intersect at focal point A? If not, draw the new focal point and label it focal point B. Make sure you also remember to sketch in the concave lens as well.
Can you think of anything that using lenses to change the direction of light rays would be helpful to? What? Give some examples below:
When finished with the lab, make sure you place all materials back where they were and hand in all lab sheets.