Electromagnetic Induction

FARADAY'S ELECTROMAGNETIC INDUCTION
Online Treasure Hunt
For High School Students Taking Physics (Science & Technology IV)

By: Ronor P. Escabarte

MOGCHS Faculty

Introduction

There are many application of electromagnetic induction. For example, the cassette tape is a magnetized tape. When played on a cassette player, the tape moves over a tiny coil and a small current is generated. The current is made bigger by the amplifier and is eventually fed to the loud speakers.

Electric guitars have “pick-ups” which are actually rows of magnets with coils around them. This magnetizes the strings and when the string vibrates current is induced in the coils.

Electric generators, transformers, rechargeable batteries. These are just some applications of electromagnetic induction.

To introduce the day’s lesson, recall Oersted’s remarkable discovery. In 1820, Hans ChristianOersted, a physics professor discovered in a classroom demonstration that an electric currentdeflects a compass needle. This shows that current produces magnetic field.
“Can the reverse of this phenomenon happen? Can magnetic field also

produce current?”

In today’s lesson we will find out who discovered electromagnetic induction, what it is, and why it is considered “a landmark in applied science”.

The lesson requires you to browse through some Web pages in which you will find out something about electromagnetic induction. A series of questions will guide your reading. Answers to the questions can be found in the Web pages, which are listed at random (and not according to the order of questions). Write your answer on the provided answer sheet and submit it after your schedule laboratory time.

You will work on by pair in answering the questions. Assign one member to take down notes and the other to write the answer in the provided answer sheet. Make sure you read between lines and be able to answer the questions accurately. Each question is 5 points each.

After successfully finding all the answers, move on to the Big Question.

Questions

1. Electromagnetic induction involves both electricity and magnetism. Which of the two is induced in the process and which one does the inducing? And what is another way of saying “to induce”?

2.In Faraday’s experiment, is it necessary to draw the magnet entirely into the coil? Why or why not?

3.Why is the principle of induction considered “a landmark in applied science”?
Consider the timeline of discoveries in electromagnetism (given in one of the websites below).

4.What is one insight you can form from looking at the timeline?

5. The invention of the dynamo was made possible by the discovery of electromagnetic

induction. What is the significance of the dynamo?

6.What invention by Faraday is the precursor of the modern transformer?

7.What is one of the medical applications of Faraday’s discovery of induced currents?

Resources

http://www.regentsprep.org/Regents/physics/phys03/dinduction/indapart.htm

http://www.electricityineducation.co.uk/60W/history/faraday.html

http://en.wikipedia.org/wiki/Transformer

http://www.geocities.com/SiliconValley/Circuit/1858/farad11e.htm

http://en.wikipedia.org/wiki/Electrical_generator

http://micro.magnet.fsu.edu/electromag/java/faraday2

http://www.phy.hr./~dpaar/fizicari/xfaraday.html

The Big Question

Form a group consisting of five members and design a simple activity on electromagnetic induction using the following materials: coil of wire, bar magnet and current detector. Sumbit your output for the big question on December 3, 2007

Writing An Investigatory Project

HOW DO WE WRITE THE RESEARCH PAPER?
by: Ronor P. Escabarte
 Science Faculty, MOGCHS

A science investigatory project ends with a report. It is also known as the technical paper.

OUTLINE FORMA. TITLE- catch the attention
- concise
- accurate
- descriptive
- self-explanatory
The phrase “A Study to Show” should be avoided, because in research you do not seek to prove something, but rather to impartially find an answer.

B. ABSTRACT
- short paragraph of not more than 200 to 250 words
- gives the essential or principal features of the project study
- descriptive
- informative

C. INTRODUCTION
This section includes the following parts:
a. Background of the Study
- presents the reasons that led the investigator to launch the study
- a historical background maybe given
- may state some observations & other relevant conditions that prompted the investigator to
explore the problem

Some guide questions while writing this part of the paper:
- Why did I select this research project?
- Are there others who have done similar studies?
- What have the others done or not done that moved or spurred me to work on this problem?
- What are my own observations which are relevant to the study?
- Will the results of the study make any contribution in the attainment of a better quality of life?
b. Statement of the Problem/Objectives
- the nature & scope of the problem should be presented with clarity

Two Types of Objectives maybe stated:
1. General Objective – this is related to the problem as given in the early part
2. Specific Objective – this states the purpose of each experiment conducted

c. Significance of the Study
- the importance of the study is explained in this part

d. Scope and Limitations
- states the coverage and extent of the study

Example: from “The Effect of Christmas Palm (Veitchia merrilli) Fruits in Lowering Blood Sugar Level”

( Coverage)
The researchers brought a 2-month old puppy in the MCA clinic (Marlito C. Aruta)
for blood analysis. They used the fruits of Christmas palm collected from North Poblacion, Naga, Cebu.

(Limitation)
The study does not cover the idea of what would be the effect of the product in the case of diabetes. The study focuses on the effect of the product to the sugar level and if it could be
a possible cure to lower the level of blood sugar

e. Review of Related Literature
- Sufficient background information should be presented for readers to understand and evaluate the results of the present study and theories written on the topic should be included.

D. Methodology
- provides enough details so that a competent worker can repeat the experiments.
a. Materials/Equipments
-the exact technical specifications, quantities and source of method of preparation for all materials used should be given.

Specifically, built equipment used in the study must be described and the description accompanied by a picture.

b. Treatment/General Procedure
- the manner and sequence by which each experiment or set of observations were done or how measurement were obtained should be described in detail.

E. Results and Discussion
- this maybe divided into sub-sections describing each set of experiments or observations.
a. Findings – the data maybe presented in full and discussed descriptively in the text or these maybe summarized in tables, pictures & graphs.

b. Analysis of Data
- the interpretation of findings are discussed and the significant features shown in the tables, figures or graphs are pointed out.

F. Conclusions
- the general truth implied or illustrated by the results should be clearly stated. The evidence based on the results should be summarized for each statement.

G. Recommendations
- consists of suggestions on future actions such as a new direction of research or further experiments to be performed, practices that might be adapted or discarded in order to attain certain goals or objectives.

H. Bibliography – a list of the references used in guiding the research work and writing the paper.

Research Paper
The research paper should contain the following:
a.Problem/s
b.Objectives
c.Method & Procedures (described in detail)
d.Results
e.Conclusions & Recommendations
f.Bibliography ( at least 3 major references

ETHICS STATEMENT
Scientific fraud and misconduct are not condoned at any level of research or competition. Plagiarism, use or presentation of other researcher’s work as one’s own, forgery of approval signatures and fabrication or falsification of data or approval dates will not be tolerated. Fraudulent projects are disqualified for the competition.

Tips in the Format
-Must be typewritten in Times Roman style
-Double-spaced in short bond paper (8” x 11”), font size 11
-The Acknowledgement should contain the names of people and agencies that helped in the conduct of the work described.
-The Table of Contents lists the different parts of the whole report with the corresponding page number of each part. The wording and grammar of the chapter titles, heading and title of tables & figures should be consistent.

How do we PRESENT OUR INVESTIGATORY PROJECT In the Science Fair?
Qualifications of a Judge in the Science Fair

a. Holder of a bachelor’s degree with specialization in any of the scientific discipline.
b. Employee of any of the science agencies or cooperating agencies of the Science Fair.
c. May be a professor in a college or university but is not directly connected with any of the schools participating in the Science Fair.
d. Preferably must have had previous experience
as a judge in a Science Fair.
e. Must be an expert in his own field of discipline.

CRITERIA for JUDGING EXHIBITS/PROJECTS

A. The project develops the investigator’s capacities in the discipline of science & scientific endeavor.

1. Creativity, originality & resourcefulness---- 30%a. Does the project show the investigator’s creative ability in presenting the problem?
- the approach to solving the problem?
- the analysis and interpretation of data?
- the use of equipment?
b. Is the project a new design or a new combination of facts and processes?
- No project is original in all aspects, however, the credit for creativity and originality lies in the new idea shown in the work. This may include whatever innovations were introduced to an already known fact or process.

c. What evidence indicates that the investigator has shown cleverness in finding ways & means to workout his project.

2. Intellectual Honesty & other Moral Values 10%How honest is the project investigator in the preparation?

3.Thoroughness & Skill 30%a. As a whole, does the project answer the problems that initiated the study or research?
b. Does the project carry out its purpose to completion within the scope of its original aim?
c. How completely has the problem been covered in the project?
d. Are the conclusions based on a single experiment or on replication?

Thoroughness and Skill continued:

e. Is there available scientific literature in the selected field?
f. Are there other approaches or theories concerning the project?
g. How long did it take to finish the project?
h. Has the investigator emphasized important details?
i. Did the investigator compare and contrast the results obtained?
j. Have controls been used?

4. Clarity of Presentation

a.Is the problem stated clearly?
b.How sufficient are the data presented?
c.How clearly is the project discussed?
d.How was the oral defense of the project during the Science Congress?

B. The project contributes to the advancement of Science and Technology.

1. Applicability of Scientific Principles 20%a. Does the project utilize any scientific principle?
b. How often are the scientific principles used?
c. Is there already an existing device of the same kind that is used by the investigators? If there is, was it a modification or an exact duplicate?

Recipe for success: study while others sleeping; work while others are loafing; prepare while others are playing; dream while others are wishing.”
-William A. Ward-

General Applications: Electricity and Magnetism

Electric motors involve rotating coils of wire which are driven by the magnetic force exerted by a magnetic field on an electric current. They transform electrical energy into mechanical energy.

Answer the following questions by clicking on the link provided below each question.
1. How Does an Electric Motor Work?
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/mothow.html#c1

2. How does a DC motor works? Explain its operation.
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motdc.html#c1

3. How does an AC Motor differ from that of a DC Motor?
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/motorac.html#c1

4. Will the bird on the high voltage wire be shocked?
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/watcir2.html#c4

5. Where will lightning strike?
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/lightning.html#c1

6. Cite a detailed discussion of the operation and application of a transformer?
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/transf.html#c1

7. What happen to the electric charge in household circuits?
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/hsehld2.html#c1

Electromagnetic spectrum

websites about electromagnetic spectrum:

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

Sample Investigatory Projects in Physics

To view the sample of IP in Physics, follow the directions below:

CLICK THE FOLLOWING:

1. Start
2. My Network Places
3. Documents on Mainserver
4. ARPE Folder
5. Select any topic of your interest.

Remember to pass your written output on Monday , August 13, 2007
Trial Product can be submitted too. It depend on availability.

Physcis Investigatory Manual

Physics Investigatory Project Manual

Structured

Title

Situation (paragraph form)

Problem (Question Form; 1 or 2)

Hypothesis (es)

Related Studies (Optional)

Experimental Design

Dependent Variables

Independent Variable

Setups (paragraph with or without diagrams or tabulated)

Materials

Procedure (detailed)

----------------------------------------------------------------
(Execution to be done by the students. The following to appear in the students report.

Results and Discussion

Conclusion (by the students)


Semi-structured

o Title
o Situation (paragraph form)
o Problem (Question Form; 1 or 2)
o Hypothesis (es)

(Related studies-optional; experimental design and execution to be done by the student)

Unstructured
o Title
o Situation (paragraph form)

(The rest to be done by the students will include Review of Related Studies; Final work for exhibition in a Science Fair or presentation in a Science Congress.)

GUIDE FOR INVESTIGATORY PROJECT IN PHYSICS

INVESTIGATIONS IN PHYSICS

Introduction

The investigations included in this manual are both experimental and extended. They are experimental in the sense that they will be based on qualitative or quantitative observations of some phenomena and deductions made by you, the student. They are extended in that more time (at least a month) than a typical physics experiment would be required to undertake them.

Some samples included in this manual are structured. You are told exactly what to do and the questions you need to consider. Others are semi-structured. In these samples, the problem situation is described but the experimental design is left to you. However, some clues or questions to consider are included. This type of investigation provides a much needed challenge for you to think more independently and thereby gain satisfaction in achieving something of your own. Those included may be linked with the experiments and activities you may have done in class.

In a third type called open-ended investigations, only the problem is described. You are given the freedom of choosing the problem you wish to investigate. Or only the general topic is given and it is up to you to state the problem and design the method with which to solve the problem. A list of possible topics is provided.

Why do an experimental research project?

An experimental research project may provide the only real opportunity you will have in school of applying scientific approaches to a task. It will give you useful experience in mathematical and experimental analysis and introduce you to the work of a research scientist. These are experiences you will not usually gain in carrying out structured activities. You will be doing science rather than merely learning about science. And you will find that your ability to inquire – the essential elements of an investigation—will be very useful in your occupational, domestic and personal life.

If you do have the opportunity to choose your own topic and your own design, the experience will be unique for you. It will be your own research.

The objectives of requiring you to undertake investigations are for you to:1. Develop an understanding of the principles of experimental investigations in physics.2. Develop skills in practical investigations using the principles and methods of physics.

Your tasks then are to:

1. Identify a topic that interests you1. Decide how best to investigate the topic

2. Choose the appropriate instruments and tools and decide how best to use them

3. Cope with inevitable difficulties and if necessary redefine the objectives of your investigation

4. Analyze, evaluate and discuss your results

5. Write a report

The main value of the investigation lies not so much on the result but in the experience or journey as you work through the investigation.

After your work is completed and report written, you may have the opportunity of presenting your research to your own class, to other interested students or at the Science Fair of your school. You can join the competition and who knows, you may be a winner.

Selecting a research topic

There are three methods of arriving at a topic to be researched:

a) you propose a topic of your choice and have it approved by your teacher;

b) you select a topic from a list already approved by your teacher; and

c) you are assigned a topic by your teacher.

You will gain maximum satisfaction if method

(a) is used as the project will definitely be yours.

You can choose from five different types of investigation:

1. Designing and constructing a device.

This will involve designing and constructing a device and exploring the associated physics concepts and principles. Examples of devices that may be constructed are a thermistor temperature probe, a light meter, a water sensor, etc. It is important to remember that this is not merely a construction exercise. The emphasis must be on using physics ideas and methods to (a) analyze the purpose of the device,

(b) design a device which will achieve the purpose,

(c) construct the device and

(d) make it work as desired (that is test it and collect useful data).

2. Investigating the operation of a device

The emphasis in this type of investigation should be on investigating the device, not building it. Some typical questions that may be considered are: What does it do? How does it do it? How well does it do it? What sets the limits of its operation? How can it be improved?

3. Solving a scientific or technological problem

This type of investigation can become relatively open ended. It is important that the problem is specifically defined.

1. Investigating a physical phenomenon

This style of investigation allows you to examine physical phenomena such as the formation of rainbows, resolution of pin-hole cameras, production of sound by humans and by musical instruments, etc. Again this type of investigation can become relatively open-ended so you will need to limit the scope of the investigation to suit the time available.

2. Investigations that extend your understanding of a specific subject area by the process of gathering, collecting and synthesizing physics information and physics ideas from various sources. The topics chosen may be related to the following areas:

(a) everyday situations such as the use of remote controls in changing TV channels, digital

recording techniques;

(b) other physics related forms of knowledge such as concepts in biophysics related to improving

athletic techniques;

(c) issues of social or personal significance such as the impact of compulsory use of seatbelts –

why was a law passed? How does it reduce/prevent injury in a vehicular accident? Or you

may be interested in the physics involved in their design or other physics issues associated

with safety on the road.

(d) technological applications such as the physics and technological applications of the laser;

technological advances in sporting equipment or in medical imaging.

Planning the investigation

1. Keep a logbook.

The logbook will be your essential companion from the selection of a topic to the completion of your investigation. In the planning stage use it to record possible topic, detailed plans and diagrams of experimental setup.

2. Generating suggestions -

a. Think beyond the laboratory. Consider your favorite sport, past time or hobby. Is there some aspect of it that is related to physics, which you can investigate?

b. Is there something at home or in your community/neighborhood that could form the basis of your investigation?

c. Is there something that you have studied in physics that you would like to study more deeply?

d. If it is a group project, brainstorm with the members of your group.

e. No one expects you to be an expert on a topic before you investigate or even afterwards. Consult resource materials or specialists before you can fully specify the actual problem you intend to solve.

3. Designing the investigation. Once you have proposed a topic, the next step is to devise a design or a method by which the investigation can be done. Brainstorm with your group alternative ways of tackling the investigation. Here are some points to consider:a. What specific questions do you want to answer?What do you think the answer will be? You are now generating the hypothesis or guess that you test. Stating an hypothesis may not be part of all investigations. However, you may have some expectations.

a. Do you have sufficient information to get underway? If not consult resource materials.

b. What equipment will be needed to carry out the investigation?a. How will you use the equipment to answer your question? What qualitative observations will be necessary? What measurements will you need to take? What will you do with these measurements? These are the questions at the heart of your experimental design.

1. Background reading and consulting. To come up with a suitable design you may need to do some background reading on your chosen topic. Ask help from your librarian or your teacher in using catalogues, computer databases, subject indices, abstracts and reviews. Record the resource materials/persons where you obtain useful information.

Carrying out the investigation
You have chosen a topic, specified exactly what you are to do, and decided how you are going to do it. The next step is to carry it out. At this point, the logbook is very important.
Most of the activities you have done consist of well-tested, structured experiments in which the desired results are reached smoothly. In an investigation this will not be so. Investigations may provide you with many unfamiliar experiences.

Here are some likely situations that you may encounter and ways of dealing with them.

(a) It would be normal to run into difficulties.

Using your imagination and perseverance in solving such difficulties is a very important part of research and a source of considerable satisfaction.

(b) Seek help if you need to from resource materials and people.

(c) Do not feel bad about making mistakes. It needs intelligence to recognize that you have made one.

(d) Once you are right into the project, you may find it necessary or desirable to modify, restrict, or extend the aims you have set for yourself. Be flexible but discuss any major change with your teacher.

(e) In some cases, it may not be possible to achieve the aim you set due to time and resources available. Realize that it is definitely a valuable exercise if you have attempted to work along logical lines and sensible use of your current scientific knowledge, the time allocated and the materials available.

(f) Beware of stockpiling. It is important to process data as soon as it has been collected. Such analysis will often suggest that certain readings need to be checked additional ones made or perhaps a new direction take.

Writing a research report

You may produce a report in three ways:

(a) a written report

(b) an oral report or

(c) a poster report.

Here are the most common parts of a research report. Your teacher will tell you which of these you will include in yours:

(a) Title page – includes the title of the investigation briefly stated, the names of the writers, the purpose for which the report is submitted, the date the research was completed.

(b) Abstract or synopsis- a statement of the specific problem investigated and the main conclusions reached

(c) Content- contains the details of the investigation. The main body covering the procedure, observations and deductions should appear subdivided into suitably labeled sections or chapters.

(d) Introduction – contains what motivated you to do the investigation or some background information

(e) Aim(s) – state exactly what you set out to investigate. If more than one, number them.

(f) Procedure, observations and deductions- the body of your report. This should includei. Clear explanation of what you attempted to doii. Description of materials usediii. Any hypotheses you set up and you went about testing themiv. Difficulties you encountered and how you overcome themv. Qualitative and quantitative observations madevi. Analysis of data and observationsvii. Conclusions made at various stages

(g) Summary of findings – here you should draw together the conclusions made at various stages, restating the findings, the limitations and possibly further associated research suggested.

(h) Acknowledgements

(i) Reference or bibliography

(j) AppendicesPreparing your poster

The essential components include·

1. A title.
2. Name(s) of the researcher(s)·
3. Aim(s) of the project·
4. Arrangement of equipment, including a labeled diagram or photograph·
5. A brief description of what you did·
6. Your findings including significant tables and graphs if any and·
7. Limitations of your results

In making your poster, consider·

• The maximum dimensions of an acceptable poster·
• How they can be attached to the display board or wall·
• Legibility from about 1 or 2 meters away·
• Attractiveness

Treasure Hunt: Study of Light and It’s Properties

Online Treasure Hunts Study of Light and It's Properties

Authored by: Ronor P. Escabarte

Misamis Oriental General Comprehensive High School

Don . A. Velez, St., Cagayan de Oro City, Philippines

ronescabart@yahoo.com.ph

Introduction

In your life you've probably encountered some neat phenomenon about light. Such examples might include the reflection of light rays, or questions about the speed at which light travels. In this activity, we will learn about light and energy. "Energy?" you might ask, well it turns out that light has a relationship to energy and vice-versa.

By clicking on the web resources below you will interview some interesting people, like the most brilliant Albert Einstein!At the end of this lesson , we should know what light is and what cool applications of light are used everyday. So, to learn more about light, click on the resources and read silently.

At the end of the first topic you are required to answer the mastery quiz . While reading between lines in the slide show presentation you will encounter some questions which you need to answer in order to proceed to the next topic. After reading with comprehension answer the following questions .

This is an individual activity, therefore you are expected to answer the questions independently based on your own understanding. Use one whole sheet of paper as answer sheets and you may take down notes for your future reference. Start reading now and enjoy hunting.

Questions

Interference
1. What brings about the striking colors we see in soap bubbles? How does it happen?
2. When do waves reinforce each other? When do waves annul each other?
3. What causes the spectrum of colors seen in gasoline splotches on a wet street? Why are these not seen on a dry street?

Diffraction
1. What happen when light pass around obstacles?
2. Do sharp objects cast sharp shadows?
3. Is diffraction more pronounced through a small opening or through a large opening?

Polarization
1. Can Polaroid sunglasses protect our eyes from intense glare? How do Polaroid sunglasses protect our eyes from the strong reflections of sunlight?
2. What is the advantage of Polaroid sunglasses over regular sunglasses?

Light
1.What is light? Is light a matter? Explain.
2. How light is measured?Light Duality1. What evidence can you cite for the wave nature of light? For the particle nature of light?

Reflection
1. What does incident light that falls on an object do to the electrons in the atom of an object?

Refraction
1. How does the angle at which a ray of light strikes a prism compare with the angle at which it passes out the other side?
2. Does refraction make a swimming pool seem deeper or shallower?

Dispersion
1. What prevents a rainbow from being seen as complete circles?
2. Does a single raindrop illuminated by sunlight disperse a spectrum of colors?

Total Internal Reflection
1. What is meant by critical angle?
2. When is light totally reflected in a diamond?
3. Light normally travels in straight lines, but it “bend” in an optical fiber. Explain

Lenses
1. What kind of lens can be used can be used to produce a real image? A virtual image?

Web Resources:

INTERFERENCE, DIFFRACTION, POLARIZATION
Slide show presentation about INTERFERENCE, DIFFRACTION, and POLARIZATIONfound in my computer dost02(D)( click this to answer questions IN INTERFERENCE, DIFFRACTION, POLARIZATION)

Directions:
1. Just click start
2. Then my computer.
3. Select and open dost02(D)
4. Just click the folder DOST, then select the topics mention above.

LIGHT
http://library.thinkquest.org/11924/light.html

( click this to answer question 1 : LIGHT) Slide show presentation ABOUT WHY DO WE STUDY LIGHTfound in my computer dost02(D) ( click this to answer question:2 LIGHT)
Directions:
1. Just click start
2. Then my computer.
3. Select and open dost02(D)
4. Just click the folder DOST, then select the topics mention above

REFLECTION , REFRACTION, DISPERSION, TOTAL INTERNAL REFLECTION & LENSES. LIGHT DUALITY

http://sol.sci.uop.edu/~jfalward/physics17/chapter12/chapter12.html

( click this to answer question 1 : REFLECTION, questions 1-2: REFRACTION, 1-2 IN DISPERSION, 1-3 TOTAL INTERNAL REFLECTION, 1 IN LENSES)

The Big Question
Make up a multiple-choice questions that would check a classmate's understanding of reflection, refraction, diffraction, interference, and polarization. ( five questions per topic)

refraction of light

Refraction at a Boundary
Refraction and Sight
In Unit 13 of The Physics Classroom, it was emphasized that we are able to see because light from an object can travel our eyes. Every object that can be seen is seen only when light from that object travels to our eyes. As you look at Mary in class, you are able to see Mary because she is illuminated with light and that light reflects off of her and travels to your eye. In the process of viewing Mary, you are directing your sight along a line in the direction of Mary. If you wish to view the top of Mary's head, then you direct your sight along a line towards the top of her head. If you wish to view Mary's feet, then you direct your sight along a line towards Mary's feet. And if you wish to view the image of Mary in a mirror, then you must direct your sight along a line towards the location of Mary's image. This directing of our sight in a specific direction is sometimes referred to as the line of sight.
As light travels through a given medium, it travels in a straight line. However, when light passes from one medium into a second medium, the light path bends; refraction takes place. The refraction occurs only at the boundary. Once the light has crossed the boundary between the two media, it continues to travel in a straight line; only now, the direction of that line is different than it was in the former medium. If when sighting at an object, light from that object changes media on the way to your eye, a visual distortion is likely to occur. This visual distortion was witnessed in The Broken Pencil activity performed in class. A pencil was submerged in water and viewed from the side. As you sighted at the portion of the pencil located above the water's surface, light travels directly from the pencil to your eye. Since this light does not change medium, it will not refract. As you sighted at the portion of the pencil which was submerged in the water, light traveled from water to air (or from water to glass to air). This light ray changed medium and subsequently underwent refraction. As a result, the image of the pencil appears to be broken. Furthermore, the portion of the pencil which is submerged in water appears to be wider than the portion of the pencil which is not submerged.
Quite obviously, these observations can be explained by the refraction of light. In this case, the only light which undergoes refraction is the light which travels from the submerged portion of the pencil, through the water, across the boundary, into the air, and ultimately to the eye. At the boundary, this ray refracts. The eye-brain interaction cannot account for the refraction of light. As was emphasized in Unit 13, the brain judges the image location to be the location where light rays appear to originate from. This image location is the location where either reflected or refracted rays intersect. The eye and brain assume that light travels in a straight line and then extends all incoming rays of light backwards until they intersect. Light rays from the submerged portion of the pencil will intersect in a different location than light rays from the portion of the pencil which extends above the surface of the water. For this reason, the submerged portion of the pencil appears to be in a different location than the portion of the pencil which extends above the water. The diagram at the right shows a God's-eye view of the light path from the submerged portion of the pencil to each of your two eyes. Only the left and right extremities (edges) of the pencil are considered. The blue lines depict the path of light to your right eye and the red lines depict the path of light to your left eye. Observe that the light path has bent at the boundary. Dashed lines represent the extensions of the lines of sight backwards into the water. Observe that the these extension lines intersect at a given point; the point represents the image of the left and the right edge of the pencil. Finally, observe that the image of the pencil is wider than the actual pencil. A ray model of light which considers the refraction of light at boundaries adequately explains the broken pencil observations.
The broken pencil phenomenon occurs during your everyday spear-fishing outing. Fortunately for the fish, light refracts as it travels from the fish in the water to the eyes of the hunter. The refraction occurs at the water-air boundary. Due to this bending of the path of light, the fish appears to be in a location where it isn't. A visual distortion occurs. Subsequently, the hunter launches the spear at the location where the fish is thought to be and misses the fish. Of course, the fish are never concerned about such hunters; they know that light refracts at the boundary and that the location where the hunter is sighting is not the same location as the actual fish. How did the fish get so smart and learn all this? Because they live in schools.
Now any fish who has done his/her physics homework knows that the amount of refraction which occurs is dependent upon the angle at which the light approaches the boundary. We will investigate this aspect of refraction in great detail in Lesson 2. For now, it is sufficient to say that as the hunter with the spear sights more perpendicular to the water, the amount of refraction decreases. The most successful hunters are those who sight perpendicular to the water. And the smartest fish are those who head for the deep when they spot hunters who sight in this direction.

Since refraction of light occurs when it crosses the boundary, visual distortions often occur. These distortions occur when light changes medium as it travels from the object to our eyes.