Download Electrostatic Forces, Fields, Energy, and Interaction

Physics
HS/Science
Unit: 08
Lesson: 01
Suggested Duration: 10 days
Electrostatic Forces, Fields, Energy, and Interaction with Matter
Lesson Synopsis:
This unit develops an understanding of electrostatics by the use of demonstrations, simulations, and modeling. The
general theme is that the current model of matter consisting of electrically neutral atoms composed of charged particles is
integral to the understanding of electrical forces. The lesson begins with traditional activities of charging objects by friction
and comparing electrostatic forces to magnetostatic forces. The traditional experiments are explained in terms of the
model of an atom, and the “attract and repel force rules” are explored and expanded. Devices to create, store, and
measure charge are utilized in experiments. The formal theory of Coulomb’s law is introduced, and problems are assigned
utilizing that theory. Elements of the historical development of electrostatics and planetary model of the atom are
researched, and students have an assignment describing contributions of historically important scientists. Additional
concepts of electric fields, potential difference, and properties of conductors and insulators are developed through
experiment, demonstration, and discussion.
TEKS:
P.5
P.5A
P.5C
P.5E
P.6
P.6B
The student knows the nature of forces in the physical world. The student is expected to:
Research and describe the historical development of the concepts of gravitational, electromagnetic, weak nuclear
and strong nuclear forces. Supporting Standard
Describe and calculate how the magnitude of the electrical force between two objects depends on their charges
and the distance between their centers. Supporting Standard
Characterize materials as conductors or insulators based on their electrical properties. Supporting Standard
Science concepts. The student knows that changes occur within a physical system and applies the laws of
conservation of energy and momentum. The student is expected to:
Investigate examples of kinetic and potential energy and their transformations. Readiness Standard
Scientific Process TEKS:
P.1
P.1A
P.2
P.2F
P.2J
Demonstrate safe practices during field and laboratory investigations.
The student uses a systematic approach to answer scientific laboratory and field investigative questions. The
student is expected to:
Demonstrate the use of course apparatus, equipment, techniques, and procedures, including multimeters
(current, voltage, resistance), triple beam balances, batteries, clamps, dynamics demonstration equipment,
collision apparatus, data acquisition probes, discharge tubes with power supply (H, He, Ne, Ar), hand-held visual
spectroscopes, hot plates, slotted and hooked lab masses, bar magnets, horseshoe magnets, plane mirrors,
convex lenses, pendulum support, power supply, ring clamps, ring stands, stopwatches, trajectory apparatus,
tuning forks, carbon paper, graph paper, magnetic compasses, polarized film, prisms, protractors, resistors,
friction blocks, mini lamps (bulbs) and sockets, electrostatics kits, 90-degree rod clamps, metric rulers, spring
scales, knife blade switches, Celsius thermometers, meter sticks, scientific calculators, graphing technology,
computers, cathode ray tubes with horseshoe magnets, ballistic carts or equivalent, resonance tubes, spools of
nylon thread or string, containers of iron filings, rolls of white craft paper, copper wire, Periodic Table,
electromagnetic spectrum charts, slinky springs, wave motion ropes, and laser pointers.
Organize and evaluate data and make inferences from data, including the use of tables, charts, and graphs.
P.2K
Communicate valid conclusions supported by the data through various methods such as lab reports, labeled
drawings, graphic organizers, journals, summaries, oral reports, and technology-based reports.
P.3
The student uses critical thinking and scientific reasoning, and problem solving to make informed decisions
within and outside the classroom. The student is expected to:
P.3A
P.3D
P.3E
©2012, TESCCC
The student conducts investigations, for at least 40% of instructional time, using safe, environmentally
appropriate, and ethical practices. These investigations must involve actively obtaining and analyzing data with
physical equipment, but may also involve experimentation in a simulated environment as well as field
observations that extend beyond the classroom. The student is expected to:
In all fields of science, analyze, evaluate, and critique scientific explanations by using empirical evidence, logical
reasoning, and experimental and observational testing, including examining all sides of scientific evidence of
those scientific explanations, so as to encourage critical thinking by the student.
Explain the impacts of the scientific contributions of a variety of historical and contemporary scientists on
scientific thought and society.
Research and describe the connections between physics and future careers.
01/10/13
page 1 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Performance Indicator(s):
•
Complete a lab report describing, explaining, and analyzing electrostatics demonstrations and phenomena in
terms of the atomic structure of matter, principles of conservation of charge, electric forces, electric fields, and
electrostatic energy. (P.2K; P.5C, P.5E; P.6B)
1E; 4J
•
Research and describe in a summary the contributions of Franklin, Millikan, and Coulomb in the development of
electrostatics and atomic structure theory. (P.3D; P.5A)
4I; 5F
Key Understandings and Guiding Questions:
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Electrical properties of matter include insulation and conduction.
— What makes an object a good insulator or a good conductor?
The development of electrostatic theory and the atomic model of matter are closely related.
— How does our atomic model of matter help us understand electrostatic phenomena?
— How can we use electrostatic phenomena to confirm our atomic model of matter?
The concepts from “mechanics” of forces, fields, and energy also describe the electrical interactions of charges.
— What are the similarities between gravitational quantities properties and electrical phenomena?
— How will studying mechanics help in the study of electricity?
The concept of electrostatics was developed through the contributions of a number of people.
— How has the concept of electrostatics changed over time?
Vocabulary of Instruction:
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charge
polarization
Coulomb’s law
insulator
potential energy
shielding
electroscope
induction
cathode ray
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electrostatics
potential difference
Coulomb
vector
magnitude
electrophorus
electromagnetic force
capacitor
electric force
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electric field
volt
conductor
law of conservation of
energy
Van de Graaf generator
Materials:
Refer to Notes for Teacher section for materials.
Attachments:
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Teacher Resource: Rotating Fork Demonstration
Handout: Charge Magnet Attract (1 per student)
Handout: Summary Report on Magnetic Pole and Electric Charge Interactions (1 per student )
Teacher Resource: Summary Report on Magnetic Pole and Electric Charge Interactions KEY
Handout: Using an Electroscope (1 per student)
Teacher Resource: Using an Electroscope KEY
Handout: Charging by Induction (1 per student)
Handout: Build an Electrophorus (1 per student)
Handout: Electric Field Hockey (1 per student)
Handout: Coulomb’s Law Applications (1 per student)
Teacher Resource: Coulomb’s Law Applications KEY
Handout: Electrical Scientists – Discover the Atom Research Paper (1 per student)
Teacher Resource: Video: Crook’s Tube Demonstration
Handout: Model of the Atom (1 per student)
©2012, TESCCC
01/10/13
page 2 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
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Handout: Electrostatic Applications (1 per student)
Teacher Resource: Electrostatic Applications KEY
Handout: Electric Fields and Equipotential Lines (1 per group)
Handout: Equipotential Surfaces Computer Lab Activity (1 per group)
Teacher Resource: Equipotential Surfaces Computer Lab Activity KEY
Handout: Electric Fields in a Parallel Plate Capacitor (1 per student)
Handout: Electric Fields in a Parallel Plate Capacitor Lab Report KEY
Teacher Resource: Van de Graaff Generator Demonstrations
Handout: Properties of Conductors (1 per student)
Teacher Resource: Video: Sharp Points
Teacher Resource: Video: Faraday Cages
Resources and References:
•
Suggested Websites:
• Website Videos:
• http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html (Use the index in the right column to find the
demonstrations.)
• http://amasci.com/emotor/vdg.html
• Van de Graaff Generator Demonstrations: http://www.amasci.com/emotor/vdgdemo.html#thr
• Rutherford Experiment: http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf
• Millikan Oil Drop Experiment:
http://highered.mcgrawhill.com/sites/0072512644/student_view0/chapter2/animations_center.html
• Simulations:
• PhET group at the University of Colorado at Boulder: http://phet.colorado.edu/new/index.php.
• Balloon and Static Electricity: http://phet.colorado.edu/new/simulations/sims.php?
sim=Balloons_and_Static_Electricity
• Electrostatic Hockey Program: http://phet.colorado.edu/new/simulations/sims.php?
sim=Electric_Field_Hockey
• http://micro.magnet.fsu.edu/electromag/java/rutherford/
• Charges and Fields: http://phet.colorado.edu/new/simulations/sims.php?sim=Charges_and_Fields
Advance Preparation:
1. Make sure software for simulations is installed and compatible with your computers and networks.
2. Prepare attachments as necessary.
Background Information:
Since it is not possible to see charges, electric fields, current, etc., most students have conceptual difficulty at times with
physics. It is helpful to develop a mental model about what is going on and then to test that model often. The physics may
not seem “real” to the student at first. It should be clear that much of the evidence for the atomic model of matter comes
from the study of electrostatics and that this atomic model is useful in understanding electricity and magnetism concepts.
There are many misconceptions about electricity and electromagnetism; thus, it is important that these misconceptions
are addressed as they arise in the lesson.
All magnets and therefore, magnetic fields, result from charges in motion (electrical currents) followed by the fact that
magnetic fields exert forces on moving charges. Magnetic fields are produced by moving charges and also influence the
motion of charges. If the magnetic fields are varying, as with alternating current, then the changing current produces
changing magnetic fields. These magnetic fields, in turn, produce (induce) changing electric fields as in a transformer.
Finally, light and other electromagnetic fields are a combination of changing electric and magnetic fields interacting with
(two faces of the same phenomena) each other.
GETTING READY FOR INSTRUCTION SUPPLEMENTAL PLANNING DOCUMENT
Instructors are encouraged to supplement and substitute resources, materials, and activities to differentiate instruction to address the needs of learners.
The Exemplar Lessons are one approach to teaching and reaching the Performance Indicators and Specificity in the Instructional Focus
©2012, TESCCC
01/10/13
page 3 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Document for this unit. Instructors are encouraged to create original lessons using the Content Creator in the Tools Tab located at the top of the page.
All originally authored lessons can be saved in the “My CSCOPE” Tab within the “My Content” area.
INSTRUCTIONAL PROCEDURES
Instructional Procedures
Notes for Teacher
ENGAGE – Introduce the Topic with a Demonstration and Questions
NOTE: 1 Day = 50 minutes
Suggested Day 1
1. Using the Teacher Resource: Rotating Fork Demonstration, perform the
demonstration. This activity will take approximately 10 minutes.
Ask:
• What is happening – what force is causing the fork to rotate?
Do not volunteer the answer to the students unless they actually know.
Possible student responses should include magnetic and electrical
forces.
2. Project the following questions on the board, and ask students to record
them in their science notebooks. Inform students they will be learning the
answers to the questions during the next two units.
• What are the rules for electric charges and magnetic poles
attracting and repelling?
• Do magnets attract or repel charges? What is the rule?
• What color are charges?
• What do they weigh?
• What reaches out and causes the force which causes the fork to
rotate? Can you see it?
3. Remind students of the importance of forming models to help us
understand phenomena, illustrate concepts, and also guide our predictions
in new experiments.
Ask:
• What is our model of matter? This question is just to confirm that the
students begin thinking about atoms, electrons, protons etc.
Materials:
• metal fork
• putty
• glass test tube
• ball point pen
• 3" x 3" block of wood with a hole
drilled into the center to hold the pen
• electrophorus plate
Attachments:
• Teacher Resource: Rotating Fork
Demonstration
Instructional Notes:
The purpose of the lesson is to review
electrostatic and magnetostatic
phenomena in an engaging manner,
possibly dispel some misconceptions,
and create a common set of
experiences that can be used in class
discussions. The report, discussed at
the end of the period, on magnetic pole
and electric charge interactions provides
a convenient summary of the rules for
electrostatic charges and magnets at
rest.
Determine whether you can do
electrostatics activities today by rubbing
a balloon with wool and sticking it to the
wall. (This also sets the stage for the
class.) If you cannot stick a balloon to
the wall, it is probably too humid to do a
good job with electrostatics activities.
Practice the rotating fork demonstration
before you do it for the class.
Science Notebooks:
Students record focus questions in their
notebooks to answer throughout
lessons.
EXPLORE – Magnets and Charges
Suggested Day 1 (continued)
1. Divide students into groups of 2–3. This activity will take approximately 15
minutes.
©2012, TESCCC
01/10/13
page 4 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
2. Distribute to each student a copy of the Handout: Charge Magnet Attract.
3. Instruct students to test materials with magnets and the charged rod to see
if they are attracted, repelled, or have no interaction.
4. Instruct students to fill out the chart on the handout as they test each
material.
Materials:
(per group)
• magnets – ring or bar magnets
• electrostatic kit including objects to
test with magnets (paper, tin foil,
penny, salt, pepper, paper clip, ….)
• balloon
• cellophane tape
• wool or fur
• plastic rods to create static charges
Attachments:
• Handout: Charge Magnet Attract
(1 per student)
Misconception:
• Students may think that a charged
body has only one type of charge.
EXPLAIN
Suggested Days 1 (continued) and 2
1. Facilitate a post-lab discussion in which students present the results of
their testing.
2. Ask different groups which items were attracted to magnets, which to
charges, and which to both. This activity will take approximately 25
minutes.
Notes:
• The magnets attract only steel objects – not all metal objects.
• Magnets and charges act differently. They are different quantities.
3. If necessary for clarification, demonstrate that the paper clip is attracted to
the charged rod once the paper clip is made easier to move by hanging it
by a thread.
4. Review with students: If two objects are attracted, the less massive one is
the one that will move most easily; thus, charged scotch tape is attracted
to everything. (Charge the cellophane tape by “peeling” it off of a balloon.)
Show that the charged tape is attracted to the paper clip. A 5–6 inch strip
of tape works well.
5. Instruct students to re-test the non-attracting things with charged
cellophane tape strips. They should use the non-sticky side.
6. Instruct students to correct their charts with the new information and
discuss their findings with their groups.
7. Distribute to each student a copy of the Handout: Summary Report on
Magnetic Pole and Electric Charge Interactions.
• As a class, or in groups, discuss the questions and/or perform tests
which allow students to answer the questions on the handout.
• Challenge them to find anything that is not attracted to the charged
tape.
©2012, TESCCC
01/10/13
Materials:
(teacher only)
• paper clip
• thread
(per group)
• magnets – ring or bar magnets
• electrostatic kit including objects to
test with magnets (paper, tin foil,
penny, salt, pepper, paper clip, ….)
• cellophane tape
• balloons
• wool or fur
• plastic rods to create static charges
Attachments:
• Handout: Summary Report on
Magnetic Pole and Electric
Charge Interactions (1 per
student)
• Teacher Resource: Summary
Report on Magnetic Pole and
Electric Charge Interactions KEY
Instructional Notes:
Students will find that several things are
not attracted to charges, such as the
paper clip. Indicate to students that this
result is probably due to mass and the
object is too heavy to move with the
relatively small charges in this
page 5 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
experiment. Hang a paper clip from a
thread, and show that the paper clip is
attracted to the charged rod.
The purpose of using the charged rod
first instead of beginning with the scotch
tape tester is to remind them of previous
labs (earlier in school grades) and how
they might have been confused earlier.
They may have been told the correct
answer, but their experience may not
have justified that answer.
Science Notebooks:
If students record observations in their
student notebooks, only one copy will
be needed per group.
ENGAGE – Quick Demonstrations
Suggested Day 2 (continued)
1. This activity will take approximately 15 minutes. Review yesterday’s
activities with students. Rub a balloon with wool or fur, and stick it to the
wall. Do the same thing with a balloon rubbed with plastic wrap.
2. If running water is available, a small, smooth stream of water will be
attracted to a charged rod or balloon.
Ask:
• What charge is the water (+ or -)? (Neutral)
• Since we cannot see charges but know the rules for attraction
and repulsion of charges, how do we explain that charged objects
attract neutral objects? (Neutral objects are charged both positively
and negatively, and the polarization aspect explains their attraction to
both positive and negative charges.)
• How can we tell the sign of a charged object? (By bringing it near
another object with a known charge)
• What is the sign of the charge on the balloons on the wall? (The
wool rubbed balloon will have a negative charge.)
• Are they charged the same or different? How could we find out?
(The balloon rubbed with plastic wrap acts the very same as the
balloon rubbed with wool but is positively charged and can be
determined by bringing it near another positively charged object.)
• What does the rubbing do? (Charging by friction; some things lose
electrons and some gain electrons)
3. Relate the demonstration to the discussion questions.
4. Principles also illustrated include the following, and these should be
addressed quickly.
• Insulators (The charges do not move, but remain fixed.)
• Conservation of charge
• Forces are stronger when the charges are closer (set up for
Coulombs law later).
5. Our model of matter (neutral atoms with positive and negative charges)
allows a reasonable explanation for all of the observations.
©2012, TESCCC
01/10/13
Materials:
(teacher only)
• balloon
• wool
• fur
• plastic wrap
(per group)
• wool
• plastic wrap
• cotton
• electroscope
• fur
• plastic rod
• foam cup
• glass
• vinyl strip
• acetate strip
• wood rod
• balloon
• fork
• Simulation: Balloon and Static
Electricity:
http://phet.colorado.edu/new/simulat
ions/sims.php?
sim=Balloons_and_Static_Electricity
Instructional Notes:
Today’s activities emphasize how
charged objects attract neutral objects
through polarization of the neutral
page 6 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
molecules. This leads to a discussion of
the use of electroscopes, how they
work, and how they can be used to tell
the charge sign of objects.
The Balloons and Static Electricity
simulation from the Internet should be
displayed to the class. It should be
tested prior to class.
In the simulation, the wool rubbed
balloon will have a negative charge, and
the polarization of the wall is evident.
The term polarization should be
introduced in this context.
The real balloon rubbed with plastic
wrap acts the very same as the real
balloon rubbed with wool, but is
positively charged. This is an
opportunity to discuss the importance of
models to explain what we cannot see.
It is difficult to tell the charge sign on the
balloons since simple attraction is not
sufficient. The balloons will rotate to
make the attraction if placed near to
each other. Repulsion is definitely a
charge-charge interaction, but attraction
may be between a neutral object and a
charged object.
Neutral molecules become polarized
through the attraction and repulsion of
their positive and negative charges with
the opposite charges closer and thus
attract stronger than the like charges
repel.
EXPLORE – Detecting Charges and Signs
Suggested Day 3
1. Distribute the Handout: Using the Electroscope and materials. Instruct
the students to perform the tests indicated in the activity. Allow about 35
minutes for the activity.
2. If needed, demonstrate how the electroscope works by performing one of
the tests as an example. It is important that students understand how to tell
the charge sign on objects by using the electroscope.
3. Facilitate a discussion of the lab report, and answer any questions.
4. Relate the results of this activity to the questions asked at the beginning of
class.
©2012, TESCCC
01/10/13
Materials:
(per group)
• wool
• plastic wrap
• cotton
• electroscope
• fur
• plastic rod
• foam cup
• glass
• vinyl strip
• acetate strip
• wood rod
• balloon
page 7 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
•
fork
Attachments:
•
Handout: Using the
Electroscope
•
Teacher Resource: Using the
Electroscope KEY
EXPORE/EXPLAIN – Making an Electrophorus
Suggested Days 3 (continued) and 4
1. Review the differences between these terms: conductor, insulator, nonconductor, and dielectric. Point out that the last three terms are used
interchangeably. Remind students of the properties learned so far.
Ask:
• If you wanted to store charge for later use and get it out fast, to
light a bulb or use it some other way, would you store it on an
insulator or conductor? (From a conductor, so the charge can move)
2. Inform students they will learn how to charge objects in a new way, called
induction, and will look at an early device used for storing charges.
3. Demonstrate the electrophorus, charging and discharging the plate with a
fluorescent bulb.
4. Emphasize that first, the base must be charged by friction and that this
charge is not used up. The fact that the bulb lights several times in the
demonstration illustrates this concept.
Ask:
• How much voltage is needed to light the bulb? (Over 100 volts)
• Where is the energy coming from? (The energy comes from rubbing
the wool on the plate creating a negative charge.)
5. Discuss, again, how the electrophorus is charged. Note the strip of
cassette tape will react as the plate is charged.
6. Distribute the Handouts: Charging by Induction and Build an
Electrophorus.
7. Instruct students to complete the Handout: Charging by Induction to
illustrate how to charge an electroscope by induction and verify the sign of
the charge is opposite of the inducing charge.
8. Instruct student groups to construct and demonstrate an electrophorus.
Groups should be able to show how the neon bulb can be flashed with the
electrophorus.
9. Instruct students to write a brief summary report in their student notebooks,
explaining how to charge by induction. They can use the electrophorus or
the electroscope as a specific example.
10. When students complete the investigation, collect the summary report that
explains how to charge an object by induction.
Materials:
(per group)
• electroscopes
• materials to construct an
electrophorus:
• foam plate
• aluminum foil plate
• foam cup
• cellophane tape
• cassette tape strip
• student neon bulb
• small fluorescent bulb if
available
Attachments:
• Handout: Charging by Induction (1
per student)
• Handout: Build an Electrophorus
(1 per student)
Safety Notes:
While not dangerous to most students, it
is wise to see if any students may have
medical conditions that would preclude
them from mild shocks.
Warn students that electronic devices,
such as watches and cell phones, can
be damaged by high voltage shocks.
Electrostatic activities have a high
voltage.
Check for Understanding:
The summary report will assist students
in preparation for the Performance
Indicators at the end of the lesson.
Instructional Notes:
©2012, TESCCC
01/10/13
page 8 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
The topics today include conductors,
insulators, dielectrics, charging by
induction, using an electrophorus, and
grounding.
Science Notebooks:
Students complete their summaries in
their notebooks. You can also make
group copies of the handouts and
instruct students to do the initial work in
their notebooks as well.
EXPLORE – Gravity Forces vs. Electrical Forces
1.
2.
3.
Suggested Day 4 (continued)
Facilitate a discussion of Newton's law of gravitation, and then, introduce
to students an exploration of electrostatic forces through an electrical
game simulation. This can be done by asking students questions.
Ask:
• What is a gravitational field? (A force field that exists around any
object that has mass)
• What is the source of this field? (Mass of the object)
• We know there are forces between charges, how
are they similar and different from gravity forces? (These forces
attract and repel differently. Both gravitational and electrical forces
decrease as the distance between the force increases.)
Say/Ask:
• We recognize mass as the source of gravity forces and charges
as the source of electrostatic forces.
• How do the forces between charges and masses change with
distance and with the "size" of the "sources"? (As distance
increases, the force decreases)
• Are the attraction forces as strong as the repelling forces for
charges? (Yes, they depend on distance.)
• Do the electrical forces cause motion like gravitational forces?
(Yes, if the force is strong enough.)
Distribute the Handout: Electric Field Hockey. Instruct students to read
and then discuss any questions they may have. Students are asked to
master at least the first two levels of the simulation and answer questions
about how forces interact.
4.
Divide students into small groups to conduct the investigation, and remind
them they will work in small groups, but be prepared to turn in the lab
report at the end of the period.
5.
Facilitate a class discussion in which students share their results and
discuss the following Guided Questions:
• What are the similarities between gravitational quantities
properties and electrical phenomena? (Gravitational and electrical
quantities change inversely as distance changes.)
• How will studying mechanics help in the study of electricity? (The
energy due to the position or movement of an object can be related to
electrical phenomena.)
©2012, TESCCC
01/10/13
Materials:
(per group)
• computer
• Simulation: electrostatic hockey
program:
http://phet.colorado.edu/new/simulat
ions/sims.php?
sim=Electric_Field_Hockey
Attachments:
• Handout: Electric Field Hockey (1
per student)
Instructional Notes:
Students should be familiar with the way
that gravity forces act at a distance, the
universal gravitational force equation
(Newton's gravity equation), and the
concept of a gravity field. Use this
background to introduce Coulombs law
and the electric field. The concepts and
equations are similar.
Foci for the discussion:
• There are similarities and
differences between gravitational
and electrical forces.
• These forces attract and repel
differently.
• Both gravitational and electrical
forces decrease as the distance
between the force increases.
Misconception:
• Students may think an electric field
and force is the same thing.
page 9 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
6.
Notes for Teacher
When students complete the investigation, collect the Handout: Electric
Field Hockey.
EXPLAIN – Theory Discussion
1.
2.
Following a discussion of the lab activities, a formal discussion of
Coulomb's law and the Electric field should be held. A discussion of this
theory should present the points below:
• Coulombs law is Felectric = k(q1 q2 /d2 ), where Felectric is the interaction
force between two charges, q1 and q2, where k=9x109 Nm2/C2.
Coulomb's law works ONLY for two charges and gives the value of
the force on both. The attraction force equation for opposite charges
and repulsion force equation for like charges are the same.
• The unit of charge is Coulomb, and the name of the equation is
Coulomb's law.
• If there are several charges, the total force on the target charge is the
vector sum of the Coulomb forces on that charge. In the lab, the puck
was the target charge.
• The total electric field at the location of the target charge due to all of
the other charges is the total force on that charge divided by its
charge. E = F/q - E has units of N/C and is vector in the direction of
the total force on a positive charge at that location.
• Repeating: E is the electric field at a location due to all other charges,
which are not at that location and is the force per charge at that
location in space.
• If the electric field at some location is known, then the force on a
charge at that location is F = qE.
• In electricity and magnetism, the emphasis tends to be more on the
electric field (force per charge) than the force. Similarly, the emphasis
is with potential difference which is potential energy per charge rather
than on potential energy.
• The electric field points away from positive charges and toward
negative charges. Show with diagrams.
Instructional Notes:
A possible short homework assignment
is given to solidify some of the language
and concepts. Schedule the assignment
to be due the next day.
STAAR Notes:
The Physics STAAR Reference
Materials include the formula for
Coulombs law as noted.
Provide students with the Handout: Coulomb’s Law Applications.
EXPLAIN/EXPLORE – History and Models of the Atom
1.
Suggested Days 4 (continued) and 5
Attachments:
• Handout: Coulomb’s Law
Applications (1 per student)
• Teacher Resource: Coulomb’s
Law Applications KEY
Knowing the evidence for the model of matter and how that evidence was
obtained, provides students with a deeper understanding of the model.
Ask: Encourage student answers but indicate that the history of this model
is the focus for today.
• How did we develop our model of an atom? (As technology
improved, the experimentation with the atom provided more
information about the structure of the atom)
• What holds the atom together? (Electrostatic force)
• How do we know the nucleus size, the relative mass of nucleus
and the electron? (Evidence from Rutherford’s scattering
experiment)
• Do all electrons have the same charge? (Yes, negative)
2.
Some significant persons in the story of our planetary model of an atom
are Franklin, Millikan, Coulomb, Rutherford, and JJ Thompson.
3.
Students will be researching the contributions of these scientists in
relation to the understanding of electrostatics and the model of an atom.
©2012, TESCCC
01/10/13
Suggested Days 6 and 7
Materials:
• Simulation:
http://micro.magnet.fsu.edu/electro
mag/java/rutherford/
• Simulation: Rutherford experiment
at the URL:
http://www.mhhe.com/physsci/chemi
stry/essentialchemistry/flash/ruther1
4.swf
• Millikan Oil Drop experiment at the
URL: http://highered.mcgrawhill.com/sites/0072512644/student_v
iew0/chapter2/animations_center.ht
ml
page 10 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
The Handout: Electrical Scientists – Discover the Atom Research
Paper serves a guide for the assignment.
4.
Note: This research can begin today with the teacher sharing the video,
URL, and animations with the class, and the remainder of the time can be
spent researching the contributions of the scientists. Students should take
notes on the handout to be used for completing the research paper.
5.
Project the Video: Crook’s Tube Demonstration, indicating the charge is
negative and is very light, as evidenced by the ability to alter its path
easily. The electrons are ripped from the electrode and accelerated
through a vacuum where they strike a phosphorescent screen. This gives
the appearance of a beam of electrons, however, it should be emphasized
that we see the flash on the screen, not the electrons. This is very similar
to CRT television sets. The Crook's tube demonstration video and
simulation is intended to show that all matter has electrons. These
particles come from the negative electrode (negatively charged) and are
easily deflected. We have not studied the magnetic field—moving charge
interaction, but it provides the easiest way to move the beam.
6.
Show the following URL - applet of the Rutherford scattering experiment.
Explain what is happening to the class, or let them view the site below or
both. For the Florida State URL, the slit should be opened up to allow the
alpha particles to encounter gold foil nuclei allowing large angle scattering.
The Rutherford scattering experiment disproved Thompson's plum
pudding model of an atom that contends that the positive charge
(pudding) contained electrons (raisins). The very heavy alpha particles
would not have been deflected by the light electrons and would have been
slowed down by the pudding. This was not what happened. The
backscattered alpha particles proved the gold nucleus was very heavy,
positively charged, and very small.
http://micro.magnet.fsu.edu/electromag/java/rutherford/
7.
Instruct students to view an animation with narration and explanation of
the Rutherford experiment at the URL:
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14
.swf
8.
Instruct students to view and take notes for the research paper, from a
simulation lab of the famous Millikan Oil Drop experiment at the URL:
http://highered.mcgrawhill.com/sites/0072512644/student_view0/chapter2/animations_center.htm
l
9.
Review the Handout: Model of an Atom, which can serve as a summary
sheet.
10. Facilitate a class discussion in which students reflect on the relevant
changes.
Ask:
• How does our atomic model of matter help us understand
electrostatic phenomena? (The presence of charges in the atom
and how they interact relates to electrostatic charges.)
• How can we use electrostatic phenomena to confirm our atomic
model of matter? (Electrostatic forces within the atom explain how
the atom is held together.)
• How has the concept of electrostatics changed over time? (This
©2012, TESCCC
01/10/13
Attachments:
• Handout: Electrical Scientists –
Discover the Atom Research
Paper (1 per student)
• Handout: Model of the Atom (1 per
student)
• Teacher Resource: Video: Crook’s
Tube Demonstration
Instructional Notes:
Students are aware of the model of an
atom containing a nucleus with
electrons outside, but may not
understand the evidence for this model
and how this interacts with
electrostatics. This is a good time to
develop the history and evidence for the
atomic model. We will look at some of
the people and experiments that led to
this model. Some of the story (energy
levels and spectra) will need to wait until
we get into modern physics.
Students are shown demonstrations,
assigned history writings, and are
reminded of activities in which they have
participated. The Handout: Model of
the Atom serves as a reminder to the
students for later study. It also helps
students in their research paper.
page 11 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
concept has proven that matter has two kinds of charge, all matter
has electrons, electrostatic forces hold atoms together, and charges
are distributed in the atom.)
11. Remind students to continue work on their historical research papers,
which will be due on Day 10 of this unit.
EXPLORE/EXPLAIN – Potential Energy and Potential Difference
Equations and Problems
1. Equations for potential energy, potential difference, and the related theory
are the focus for the day’s lesson.
2. In relation to a positive charge in the electric field produced by a negative
charge,
Ask:
• Where does that positive charge have more potential energy?
(Farther away)
• Where would it have zero potential energy? (Zero PE place is
normally at r = ∞)
3.
Demonstrate the voltmeter and measure the potential difference of
different sources. Make the point that the potential energy and potential
energy per charge (voltage) require a zero reference point. Hence, the
real name for voltage is potential difference (the difference in potential
energy per unit charge) between two locations. The unit for potential
difference is volt.
4.
For charges, the zero PE place is normally at r = ∞. Thus, the potential
difference - the voltage for a negative charge is a negative number which
has a larger absolute value as you get closer to the negative charge. We
use the term voltage, or potential, when we are casual - in the same way
that we use the term mileage when we mean distance between two
locations.
5.
The following set of quantitative concepts should be explained and used
while modeling calculations to aid in the basic understanding of the
material:
• Coulombs Law – force between two point charges
• Electric field from a point charge at a distance from the charge
(charge is source of E)
• Vector addition of E from more than one charge (simple geometry)
• Force on charge in that field is F = qE
• All charges are multiples of electronic charge. q = N e
• The potential energy between two point charges (the energy is in the
interaction) stress this is a scalar. U=kq1q2/r
• The number of interactions for 2 charges is 1, for 3 charges it is 3, for
4 charges it would be 6, and so on. These are scalar interactions but
may be positive or negative
• The potential difference (commonly called voltage) at a given location
for a point charge. (potential energy per charge)
• For several charges, the total potential difference at a location is the
algebraic sum of contributions from charges.
• For charged objects (not point charges, specific equations for those
objects must be used to calculate E, V, U, etc.)
• For a parallel plate capacitor, the electric field inside the plates is
constant.
©2012, TESCCC
01/10/13
Suggested Day 8
Materials:
(teacher only)
• voltmeter
• batteries of various sizes
Attachments:
• Handout: Electrostatic
Applications (1 per student)
• Handout: Electrostatic
Applications KEY
Instructional Notes:
It is possible to spend a lot of time
working electrostatics problems. They
can be difficult and tricky or straight
forward. Since not all resources (books,
Internet, worksheets, etc.) use the same
symbols for all of the quantities, you
should be careful in sending the
students to the web for tutorial help. It is
important when using formulas to use
the Physics STAAR Reference
Materials as a resource for students to
use when performing calculations.
STAAR Notes:
The Physics STAAR Reference
Materials include the formula for electric
potential energy-distance as noted.
page 12 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
6.
Notes for Teacher
Distribute the Handout: Electrostatic Applications, and instruct students
to complete the calculations.
EXPLAIN/ELABORATE – Electric Fields and Equipotential Surfaces
Suggested Day 9
Materials:
(per group)
• Simulation from PHET – Charges
and Fields:
http://phet.colorado.edu/new/simulat
ions/sims.php?
sim=Charges_and_Fields
Attachments:
• Handout: Electric Fields and
Equipotential Lines (1 per group)
• Handout: Equipotential Surfaces
Computer Lab Activity (1 per
group)
• Teacher Resource: Equipotential
Surfaces Computer Lab Activity
KEY
Instructional Notes:
Students have done some electrostatics
exploration in general, and they have
looked at the model of matter and the
history validating parts of the model.
They know Coulombs law, have made a
few simple calculations, and have been
introduced to the electric field. Today,
they explore the electric field in more
detail.
1.
Today, students explore the relationship between charges, electric fields,
and electric potential difference using a simulation. The analogy between
equipotential gravitational surfaces (a table top for example) and
equipotential electrical surfaces can be a powerful learning tool.
2.
Use the Handout: Electric Fields and Equipotential Lines to introduce
and/or review the terminology of equipotential lines or surfaces.
Perform a quick demonstration of the PHET program to assist the
students in making quick progress in the lab.
Distribute the Handout: Equipotential Surfaces Computer Lab Activity.
Assist the students in performing the investigation.
3.
4.
5.
Facilitate a class discussion in which students share their results. Clarify
any misunderstandings.
6.
When students complete the investigation, collect the Handout:
Equipotential Surfaces Computer Lab Activity.
©2012, TESCCC
01/10/13
The normal convention is that electric
fields end on negative charges and get
less strong (absolute number) as you
get farther from the charge, similar to
the gravitational field from a planet or a
Sun.
This lesson is intended to strengthen
the concept of electric field and to
connect it to the electric potential
difference. The analogy with the
equivalent concepts in the study of
gravity should still be useful. First,
establish some conventions and
common background terminology.
The analogy is that the gravity field
points down. Surfaces with the same
potential energy are horizontal. Thus,
the equipotential surfaces are
page 13 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
perpendicular to the gravity field. This is
the same with electrical quantities.
ELABORATE – Electric Fields in a Parallel Plate Capacitor
Conductors Shield Electric Fields from Outside
1. The concepts explored on this day are related to the previous activity and
the simulation is used.
2.
Ask one or more of the following questions:
• If you wanted to perform an experiment on the hazards or
benefits of electric fields on humans, how would you produce a
region with constant electric fields? This question may not
develop good responses, but can get to the point that E results from
charges and that point charge fields vary with distance. The answer
is to place the experiment within a parallel plate capacitor.
• Have you ever had trouble getting a portable radio (or cell
phone) to work inside a metal structure? Conductors shield
electric fields from the outside.
• Why do you want to be riding in an old Chevy sedan instead of a
Corvette when struck by lightning? The Chevy is made of metal,
and the Corvette is plastic; thus, the metal protects you from the
lightning. It is not that “the wheels ground” you from the charge as
some would say. In fact, you want to drain the charge away so a path
to ground is good.
3.
Remind students that capacitors are used to store electrical energy and
have other uses in electrical circuits. The parallel plate capacitor is an
important learning example in physics and illustrates a number of
concepts.
4.
Distribute a copy of the Handout: Electric Fields in a Parallel Plate
Capacitor, and instruct students to complete the investigation. This
investigation utilizes the “Charges and Fields” simulation.
5.
Instruct students to complete the handout using the simulation.
6.
Briefly discuss student findings, and answer any questions related to
electric fields and capacitors.
7.
When students complete the investigation, collect the Handout: Electric
Fields in a Parallel Plate Capacitor.
ELABORATE – Van de Graaff Generator
Materials:
(per group)
• Simulation from PHET: “Charges
and Fields”
http://phet.colorado.edu/new/simulat
ions/sims.php?
sim=Charges_and_Fields
Attachments:
• Handout: Electric Fields in a
Parallel Plate Capacitor (1 per
student)
• Handout: Electric Fields in a
Parallel Plate Capacitor Lab
Report KEY
Instructional Notes:
The Charges and Fields simulation
software is excellent in explaining the
connection between equipotential
surfaces and the direction of electric
fields.
The point of the simulation is that the
electric fields for the charges on the
inside of the conductors (capacitor
plates) are blocked by the conducting
plates. Thus, the fields are not basically
present outside the interior of the
capacitor. This is not true for the two
lines of charge in the simulation held in
place on an insulating base. This is an
important property of conductors for
static charges - electric fields are zero
within (inside) the conducting material.
Suggested Day 10
1.
Begin the class with a few demonstrations from the Teacher Resource:
Van de Graaff Demonstrations.
2.
Ask:
• What is the voltage of the Van de Graaff generator? 100 V, 1,000
V, 10,000 V, or 100,000 V? Voltages of over 100,000 are not
uncommon. To estimate, a 1 cm spark for dry air requires 30,000
volts for flat surfaces.
• Is this voltage dangerous? Why or why not? It is not dangerous
because it is current that is fatal, not voltage. The normal static
shock, which can be on the order of 10–40 kv, is not fatal because it
is very low current.
• How does the generator work?
©2012, TESCCC
Suggested Day 9 (continued)
01/10/13
Materials:
• Van de Graaff generator
• fluorescent bulb
• neon bulb
• thread
• cotton
• aluminum foil plate
• soap bubbles
• foil covered cardboard
page 14 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
If possible, disassemble to the point where students can view the
essential parts.
3.
If it is not possible to disassemble the generator, display a diagram from
a hyperphysics site and point out the essential parts:
• metallic dome
• moving belt
• sharp pointed wires on both ends (linking the belt to …)
4.
Distribute the Handout: Properties of Conductors, which is the basis for
the lecture-discussion-demonstration.
5.
Read each statement, and either discuss, illustrate, or demonstrate to
allow students to understand and believe what is occurring. Students will
take notes on the handout.
Explain how a Van de Graaff generator works, using the principles on the
sheet.
6.
7.
Perform additional demonstrations with the generator, and discuss how
the rules of electrostatics explain the demonstrations.
•
•
•
•
•
•
•
•
•
aluminum foil pieces
tissue paper strips
rice crispy cereal
piece of wire
paperclip
Internet with class display to show
Internet demonstrations
Website video:
http://hyperphysics.phyastr.gsu.edu/hbase/hframe.html
(Use index on the right column to
find demonstrations.)
Website video:
http://amasci.com/emotor/vdg.html
Website: Van de Graaff Generator
Demonstrations:
http://www.amasci.com/emotor/vdg
demo.html#thr
Attachments:
• Teacher Resource: Van de Graff
Generator Demonstrations
• Handout: Properties of
Conductors (1 per student)
• Teacher Resource: Video: Sharp
Point
• Teacher Resource: Video: Faraday
Cages
Safety Notes:
While not dangerous to most
students, check for students who
may have medical conditions that
would preclude them from mild
shocks.
Instructional Notes:
Today, the focus will be on introducing
the concept that conductors shield
electric fields from the outside. The Van
de Graaff generator is used to engage
this topic as well as the Handouts:
Properties of Conductors and
Discussion of Hollow Conducting
Sphere.
This portion of the lesson is intended to
make sure that students know the
properties of conductors, have a visual
experience to convince them that they
are true, and reinforce what is meant by
the statements.
The instructor basically reads the
©2012, TESCCC
01/10/13
page 15 of 16
Physics
HS/Science
Unit: 08 Lesson: 01
Instructional Procedures
Notes for Teacher
properties one by one and asks if this is
clear and/or provides a demonstration
or example (shown on the statement) to
clarify the concept. At the end of the
handout, these concepts are used to
explain how a Van de Graaff generator
works.
There are a number of ways to explain
that the charge goes to the outside of a
conductor. One way is to indicate that a
conductor is all at the same potential,
everything inside is at that potential, and
thus, there is no tendency for current
flow.
EVALUATION – Performance Indicators
Performance Indicators
• Complete a lab report describing, explaining, and analyzing
electrostatics demonstrations and phenomena in terms of the atomic
structure of matter, principles of conservation of charge, electric forces,
electric fields, and electrostatic energy. (P.2K; P.5C, P.5E; P.6B)
1E; 4J
•
Research and describe in a summary the contributions of Franklin,
Millikan, and Coulomb in the development of electrostatics and atomic
structure theory. (P.3D; P.5A)
4I; 5F
©2012, TESCCC
01/10/13
Suggested Day 10 (continued)
Instructional Notes:
The Performance Indicators for this unit
have been completed during this unit
and should indicate a student’s
understanding of the concepts related to
electrostatic forces.
Students can use the prior lab reports
and research paper as a reference for
completing a report that describes,
explains, and analyzes the
demonstrations and phenomena
explored in this lesson.
page 16 of 16