Download Electric Field - Spring Branch ISD

A1 Conceptual Physics
Spring 2013
Static Electricity
Chapter 32 and 33
Conceptual Physics Electrostatics Outline
Hewitt: Chapter 32 & 33
Exercises: 15 Electrostatics
Fill in the Charts completely
Variables introduced or used in chapter:
Quantity
Symbol
Charge
Test Charge
Charge on one electron
qe
Force
Distance
Electrostatic Constant
Electric Field
Work
Potential Difference
Electric Field
Units
Formula Chart*
*In Class, we will use x for horizontal motion, and y for vertical motion instead of ‘d’
Electrostatic Force
Electric Field
Potential Difference / Voltage
Electric Field
Define the following terms using COMPLETE SENTENCES:
Electrostatics
Electrical Forces
Charge
Conservation of Charge
Coulomb
Coulomb’s Law
Conductor
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A1 Conceptual Physics
Spring 2013
Insulator
Static Electricity
Chapter 32 and 33
Semiconductor
Superconductor
Charging by Friction
Charging by Induction
Charge by Polarization
Induction
Grounding
Electric Dipole
Electric Field
Lines of Force
Electric Potential Energy
Electric Potential
Voltage
Volt
Van de Graff Generator
Formula Summary:
𝐹𝑒 =
𝑘𝑞1 𝑞2
𝑑2
∆PEelectric = −q∆V
Constants:
UNITS: F (N)
𝐹
𝐸=𝑞
𝑘𝑞
𝐸 = 𝑑2
∆V = Ed
𝑊 = ∆𝑃𝐸 = 𝐹𝑑
∆PEelectric = −qEd
𝑞 = 𝐶𝑉
k= 9 x 109 Nm2/C2
q (C)
d (m)
e = - 1.6 x 10-19 C
E (N/C)
V(V)
2
μ= 10-6
PE (J) C (F)
A1 Conceptual Physics
Spring 2013
Static Electricity
Chapter 32 and 33
Homework Problems
Electric Force Problems:
1. What is the force on a positive charge of 5 x 10 -6 Coulombs that is .05 meters away
2.
3.
4.
5.
6.
7.
8.
from another positive charge of 4.5 x 10 -6 Coulombs? [81 N, repulsive]
What is the force on a negative charge of -3.4 x 10 -6 C and a positive charge of 4.0 x
10 -6 C that are .030 meters away from each other? [136 N, attractive]
What is the distance between two negative charges of 7.4 x 10 -9 C and 5.3 x 10 -6 C
that have a force of .32 Newton’s between them?[0.033 m]
What is the unknown charge if there is a force of 1 X 10 -3 Newton’s on two charges
that are .0004 meters? The other charge is 2.5 X 10 -15 C. [7.11 x 10-6 C]
Two charges, q1 and q2, are separated by a distance, d, and exert a force, F, on each
other. What new force will exist if…
a. q1 is doubled? [2x]
b. d is tripled? [ x 1/9]
c. q1 is tripled and d is doubled? [x ¾]
A negative charge of –2.0 x 10-4 C and a positive charge of 8.0 x 10-4 C are
separated by 0.3 m. What is the force between the two charges? [Attractive,
16000 N]
A negative charge of –6.0 x 10-6 C exerts an attractive force of 65 N on a second
charge 0.050m away. What is the magnitude of the second charge? [3 x 10-6 C]
A force of –4.4 x 103N exists between a positive charge of 8.0 x 10-4 C and a
negative charge of –3.0 x 10-4 C. What distance separates the charges? [0.70m]
Electric Field Problems:
9. Sketch the electric field lines around the following scenarios:
a.
b.
c.
d.
–1.0 C charge
3.4 x 10-6 C charge
1 C and –2 C charges
Dipole with 1C and -1C charges
10. What is the magnitude of an electric field where a positive charge of 5 x 10 -6 C
11.
12.
13.
14.
experiences a force of .70 Newtons? [1.4x104 N/C]
The magnitude of an electric field is 4.2 x 10 2 N/C. If the force is .90 Newtons, how
many Coulombs does the positive charge have? [.00214 C]
An oil drop weighs 1.9 x 10-15 N. It is suspended in an electric field with an intensity
of 6.0 x 103 N/C. What is the charge on the drop? [3.17 x 10-19 C]
A test charge experiences a force of 1.4 x 10-8 N at a point where the electric field
intensity is 2.0x 10-4 N/C.
a. What is the magnitude of the test charge? [7 x10-5 C]
b. Assuming the field is created by a negative charge, what is the direction of
the field on the test charge? (towards the center of the field, or away from
the center of the field?)
Electrons (q = -1.6 x 10-19 C) are accelerated by the electric field in a television
picture tube (1 x 105 N/C).
a. Find the force on an electron. [-1.6 x 10-14 N]
b. The electric field is produced by a positive charge. What is the direction of
the field on the electron?
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A1 Conceptual Physics
Spring 2013
Static Electricity
Chapter 32 and 33
Electric Potential
15. A uniform electric field has a magnitude of 250 N/C. A 12 µC (12 x 10-6C) charge
moves 0.2 m in the direction of the electric field. What is the change in electrical
potential energy of the system? [-6 x 10-4 J]
16. What is the change in electric potential energy in a lightning bolt if 35 C of charge
travels to the ground from a cloud 2000m above the ground in the direction of the
field? Assume the electric field is uniform and has a magnitude of 1.0 x 106 N/C. [-7
x 1010J]
17. A charge moves a distance of 2.0 cm in the direction of a uniform electric field
having a magnitude of 215 N/C. The change in electrical potential energy is -6.9 x
10-19 J as it moves. Find the magnitude of the charge on the moving particle. [1.605
x 10-19C]
18. If 120 J of work are done to move 1 C of charge from a positive plate to a negative
plate, what voltage difference exists between the two plates? [120 V]
19. A voltmeter reads 500 V when placed across two charged parallel plates. The
plates are 0.020 m apart. What is the electric field between them? [2.5 x 104 N/C]
20. If the uniform electric field between two parallel plates is 1050 N/C and the
potential difference across the plates is 100 V, how far apart are the plates? [0.095
m]
21. If a 0.02 C particle experiences a 40 N electric force due to the electric field it is in,
what is the strength of the electric field? [2000 N/C]
22. The electric field in the atmosphere is about 150 N/C downward.
a. What is the direction of electric force on a positively charged particle?
b. Find the electric force on a proton with charge +1.6 x 10-19 C. [2.4 x 10-17 C]
Capacitance:
23. A Capacitor has a capacitance of 1F. What is the potential difference if you have 3C
of charge on one plate: [3V]
24. A capacitor of 1μF has a potential difference of 2.0 x 10-5V. What is the charge? [2 x
10-11 C]
25. What is the capacitance of a if 2V holds 6μC of charge? [ 3 x 10-6 F]
Mixed Practice Problems:
26. Sketch the electric field lines around the following scenarios:
a. –1.0 C charge
b. 3.4 x 10-6 C charge
c. 1 C and –2 C charges
d. Dipole with 1C and -1C charges
27. What is the magnitude of an electric field where a positive charge of 5 x 10 -6 C
experiences a force of .70 Newtons? [1.4x104 N/C]
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A1 Conceptual Physics
Static Electricity
Spring 2013
Chapter 32 and 33
28. The magnitude of an electric field is 4.2 x 10 2 N/C. If the force is .90 Newtons, how
many Coulombs does the positive charge have? [.00214 C]
29. What is the electric field on a charge of 3.6 X 10 -15 C that is experiencing a force of
5 X 10 -3 Newtons? [1.389 x 1012 N/C]
30. A test charge experiences a force of 1.4 x 10-8 N at a point where the electric field
intensity is 2.0x 10-4 N/C. What is the magnitude of the test charge? [7 x10-5 C]
a. Assuming the field is created by a negative charge, what is the direction of
the field on the test charge? (towards the center of the field, or away from
the center of the field?)
31. Electrons (q = -1.6 x 10-19 C) are accelerated by the electric field in a television
picture tube (1 x 105 N/C). Find the force on an electron. [-1.6 x 10-14 N]
a. The electric field is produced by a positive charge. What is the direction of
the field on the electron?
32. A uniform electric field has a magnitude of 250 N/C. A 12 µC (12 x 10-6C) charge
33.
34.
35.
36.
37.
38.
39.
moves 0.2 m in the direction of the electric field. What is the change in electrical
potential energy of the system? [-6 x 10-4 J]
What is the change in electric potential energy in a lightning bolt if 35 C of charge
travels to the ground from a cloud 2000m above the ground in the direction of the
field? Assume the electric field is uniform and has a magnitude of 1.0 x 106 N/C. [-7
x 1010J]
A charge moves a distance of 2.0 cm in the direction of a uniform electric field
having a magnitude of 215 N/C. The change in electrical potential energy is -6.9 x
10-19 J as it moves. Find the magnitude of the charge on the moving particle. [1.605
x 10-19C]
If 120 J of work are done to move 1 C of charge from a positive plate to a negative
plate, what voltage difference exists between the two plates? [120 V]
A voltmeter reads 500 V when placed across two charged parallel plates. The
plates are 0.020 m apart. What is the electric field between them? [2.5 x 104 N/C]
If the uniform electric field between two parallel plates is 1050 N/C and the
potential difference across the plates is 100 V, how far apart are the plates? [0.095
m]
If a 0.02 C particle experiences a 40 N electric force due to the electric field it is in,
what is the strength of the electric field? [2000 N/C]
The electric field in the atmosphere is about 150 N/C downward.
a. What is the direction of electric force on a positively charged particle?
b. Find the electric force on a proton with charge +1.6 x 10-19 C. [2.4 x 10-17 C]
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A1 Conceptual Physics
Spring 2013
Static Electricity
Chapter 32 and 33
Statics Lab: #1
You take a latex balloon and inflate it. You then rub the balloon vigorously against your
hair for 20 seconds. When you try to pull the balloon away from your hair, it appears that
your hair is stuck to it. You know that latex has very tightly bound electrons, so it is NOT
going to lose electrons. What is going on between your hair and the balloon?
Picture:
a.) Who has a positive charge and who has a negative charge?
b.) Who lost and who gained electrons?
c.) Why do the two objects appear to be attached?
d.) How did you charge the balloon - by conduction, induction, or polarization?
e.) How did you charge your hair - by conduction, induction, or polarization?
Your partner in crime has done the same thing with another balloon. If you hold the two
balloons next to each other, what will they do?
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A1 Conceptual Physics
Spring 2013
Static Electricity
Chapter 32 and 33
Statics Lab #2
Procedure: This lab allows you different opportunities to see how charges are
produced, transferred, and identified in different settings.
Materials:
Styrofoam sheet
wool
fur
rubber
rod
Tissue paper
water source
balloon
wall space
Background information:
Clothes removed from a clothes dryer usually cling to each other and spark or crackle
with static electricity when they are separated. When two dissimilar materials are
rubbed together, they can become charged. Objects can acquire static electric charges
by either gaining or losing electrons. An object that gains electrons has a net negative
charge and is said to be negatively charged. An object that loses electrons has a net
positive charge and is said to be positively charged. Only those objects separated from
a ground, or Earth, by an insulator will retain their charge for any length of time.
In electricity, a “ground” is the term used to describe a conductor that allows electric
charges to dissipate from an object. For instance, you behave as a ground if you touch a
charged object. The object’s charges move through you and into the Earth. The object
is now uncharged again. Objects that are attached to a ground through a conductor will
remain uncharged, since the charge travels easily through the conductor and into the
ground and is quickly dissipated.
In this lab you will be using wool and fur to charge Styrofoam and rubber. Wool does
not have a strong affinity for its electrons and tends to lose them when rubbed against
another surface, making it become positive and the surface it has been rubbed against
negative. Fur also does not have a strong affinity for its electrons and will also lose
them to another substance when in contact with it, making the fur become positive and
the substance it is in contact with negative.
Procedure:
A. STYROFOAM AND WOOL
1.) Rub the piece of wool vigorously along the flat surface of the Styrofoam sheet
for at least 20 seconds.
2.) Hold the sheet ABOVE the arm hair of one of your group members and observe
the behavior of their arm hairs, and their physical reaction. Also listen for any
sounds.
Questions: (4.5 Each)
1.) What charge does the wool acquire after being rubbed on the Styrofoam?
2.) What charge does the Styrofoam acquire after being rubbed with the wool?
3.) What happens to the arm hairs when they are in close proximity to the charged
Styrofoam?
4.)
5.) Explain why this happens, and draw a picture to diagram what is happening
with the charges.
6.) What method of charging is demonstrated in this scenario?
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A1 Conceptual Physics
Spring 2013
B. BALLOON AND WALL
1.) Inflate a balloon.
2.) Vigorously rub the surface of the balloon with the wool.
3.) Hold the balloon so that it is touching the wall and let go.
4.) Observe what happens.
Static Electricity
Chapter 32 and 33
Questions (4.5 each)
5.) What charge did the balloon acquire after being rubbed on the balloon?
6.) What charge did the balloon acquire after being rubbed with the wool?
7.) What happened when you touched the balloon to the wall? Explain why
this happened, and draw a picture to diagram what is happening with the
charges.
8.) What method of charging is demonstrated in this scenario?
C. BENDING WATER
1.) Rub the fur along the rubber rod vigorously for at least 20 seconds.
2.) With a small stream of water coming from the water source, hold the rod
close to but not touching the water source.
3.) Observe what happens.
Questions (4.5 Each)
9.) What charge did the fur acquire after being rubbed on the rubber rod?
10.) What charge did the rubber rod acquire after being rubbed with the fur? _
11.) What happened to the stream of water when the rubber rod was held
close to it? Explain why this happened, and draw a picture to diagram what is
happening with the charges.
12.) What property of water allows it to be manipulated by another charged
object? Draw a picture of the water molecule to demonstrate your answer.
D. MAGIC WAND
1.) Touch your finger to the rubber rod to discharge the previous experiment’s
charge from it.
2.) Touch the end of the rod to the tissue paper and observe what happens.
3.) Rub the fur along the rubber rod vigorously for at least 20 seconds.
4.) Hover the end of the rod above the tissue paper and observe what happens.
Questions (4.5 Each)
13.) What was the purpose of you touching the rubber rod before you touched
the tissue paper with it?
14.) What is the word used to describe what you functioned as?
15.) What charge did the fur acquire after being rubbed on the rubber rod?
16.) What charge did the rubber rod acquire after being rubbed with the fur?
17.) What happened to the tissue paper when it was very close to the charged
rod compared to when it was touched with the neutral rod? Explain why this
happened, and draw a picture to diagram what is happening with the charges.
18.) What method of charging is demonstrated in this scenario?
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A1 Conceptual Physics
Spring 2013
E. ELECTROPHORUS
Static Electricity
Chapter 32 and 33
1.) Rub the Styrofoam insulation sheet vigorously with the wool for at least 20
seconds.
2.) Place the pie plate on top of the Styrofoam sheet. Note how the charges
separate.
Figure 3
3.) Touch the top of the plate with your finger and observe what happens.
4.) Hold the inverted Styrofoam cup and lift the pie pan off the Styrofoam sheet
without touching the plate.
5.) Touch the plate to your earlobe and observe what happens.
Questions (4.5 Each)
19.) What method of charging was demonstrated by setting the pie plate on top
of the Styrofoam sheet?
20.) The first time you touched the pie plate, you should have felt a “shock”.
What type of charges were flowing from the top of the plate to your finger?
21.) What was the overall charge on the pie plate once you picked it up by it’s
Styrofoam cup handle?
21.) When you then touched the plate to your earlobe, you should have felt and
heard another “shock”. Which type of charges were flowing from the pie plate
to your earlobe?
22.) What was the purpose of using a Styrofoam sheet to put the metal pie
plate on, and a Styrofoam cup as a handle for the plate?
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A1 Conceptual Physics
Spring 2013
Static Electricity
Chapter 32 and 33
Review – DUE BEFORE TEST
1. What is the force between two charges of 3 X 10 -23 C and 7 X 10 -7 C if they are .05
meters apart? [7.56 x 10-17 N]
2. What is the distance between two charged objects if the force is 6.2 X 10 -2
Newtons. The charges are 5 X 10 -23 C and 4.2 X 10 -15 C? [1.75 x 10-13 N]
3. What is the unknown charge if there is a force of 1 X 10 -3 Newtons on two charges
that are .0004 meters? The other charge is 5 X 10 -15 C. [3.56 x 10-6 C]
4. Two charges, q1 and q2, are separated by a distance, d, and exert a force, F, on each
other. What new force will exist if…
a.) q1 and q2 are cut in half?[x ¼ ]
b.) d is cut in half? [ x 4]
5. Sketch the electric field lines around the following scenarios:
a. +1.0C charge
b. 3.4 x 10-6 C charge
c. Dipole with 2C and -2C charges
6. What is the magnitude of an electric field where a negative charge of 3 x 10 -7 C
experiences a force of .09 Newtons? [-3x105 N/C]
7. If the electric field is 2.1 X 10 -5 N/C and the charge is 2.3 X 10 -19 C , what is the
distance that the charge is away?[0.00993m]
8. If the electric field is 3.2 X 10 -3 N/C and the distance away is .005 meters, what is
the charge of the object? [8.89 x 10-18 C]
9. A negative charge of 2.0 x 10-8 C experiences a force of 0.060 N to the right in an
electric field.
a. What is the field magnitude? [3 x 106 N/C]
b. What is the direction of the field? [Left]
10. A positive test charge of q=5.0 x 10-4 C is in an electric field that exerts a force of 2.5
x 10-4 N to the left on it.
a. What is the magnitude of the electric field at the location of the test
charge? [.5 N/C]
b. What is the direction of the electric field on the test charge?
c. If the test charge was moved closer to the center of the field, how would
the magnitude of the force exerted on it change?
11. A force of 0.053N is required to move a charge of 0.037μ C (0.037 x 10 -6 C) a
distance of 25 cm in an electric field. What is the change in potential energy
between the two points? [3.58 x 105V]
12. How much work is done to transfer 0.15 C of charge through a potential difference
of 9.0 V? [1.35 J]
13. The electric field intensity between two charged plates is 1.5 x 103 N/C. The plates
are 0.080 m apart. What is the potential difference between the plates in volts?
[120 V]
14. If 13 J of work is done on a 15 C charge, what force was applied to the charge to get
it to move 0.5 m? [26 N]
a. What is the change in potential energy of the charged particle? Why? [13 J]
b. What potential difference did the charge move across? [0.867 V]
15. A Capacitor has a capacitance of 2 F. What is the potential difference if you have 3C
of charge on one plate: [6V]
16. A capacitor of 1μF has a potential difference of 4.0 x 10-5V. What is the charge? [4 x
10-11 C]
17. What is the capacitance of a if 1V holds 6μC of charge? [ 6 x 10-6 F]
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