Download Chapter 21 Electric Charge and Electric Field

Chapter 1
 Overview of static electricity( On Electric
Force , field and, Electric potential,
capacitance and dielectrics).
 http://www.fayoum.edu.eg/nmh
E-Mail: [email protected]
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‫اجندة العام الجامعى ‪2016/2017‬‬
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‫امتحان اعمال الفصل الدراسي االول من السبت ‪ 12/11/2016‬الي الخميس‬
‫‪.17/11/2016‬‬
‫االمتحانات العمليه والشفويه للفصل الدراسي االول يوم السبت ‪24/12/2016‬‬
‫الي يوم الخميس ‪29/12/2016‬‬
‫نهايه الفصل الدراسي االولي يوم الخميس ‪5/1/2017‬‬
‫امتحانات الفصل الدراسي االول يوم االثنين ‪ 9/1/2017‬الي ‪26/1/2017‬‬
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‫‪3-10-2016‬‬
Hrs / week
Course N
o
Course Title
GEN 110
Marks
Exam
hours
Lect
Tut
Lab
Final
Y.Work
oral
Lab
Total
English Language (1)
)1( ‫لغة إنجليزية‬
2
-
-
40
10
-
-
50
2
GEN 113
Computational Linguistics
‫لغويات حسابية‬
2
-
-
40
10
-
-
50
2
GEN 114
Humanities
‫انسانيات‬
2
-
-
40
10
-
-
50
2
GEN 120
Mathematics (1)
)1( ‫رياضيات‬
4
3
-
115
20
15
-
150
3
GEN
125
Physics (1)
)1( ‫فيزياء‬
4
3
2
90
25
10
25
150
3
4
-
4
105
15
10
20
150
3
Basics of
computer science
‫أساسيات علوم الحاسب‬
CSC160
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Physics 1 Gen 125 :
Electricity
REF: Physics For Scientists And Engineers 6E By Serway And Jewett
 Ch. 1 : Overview of static electricity( Ch. 3 - Direct current and circuit
on Electric field and Gauss’ law,
Electric potential, capacitance
and dielectrics).
 Ch. 2 : Resistance and current:
2-1 Electric Current
2-2 Resistance
2-3 A Model for Electrical
Conduction
2-4 Electrical Power
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3 -1 Electromotive Force
3 -2 Resistors in Series and Parallel
3 -3 Kirchhoff’s Rules
3 -4 RC Circuits
3 -5 Electrical Meters
Inductance: Self learning
4
Physics 1 Gen 125 : Electricity
Ref: Physics For Scientists And Engineers 6E By Serway And Jewett
Ch. 4 : AC circuits:
4.1 AC Sources
4.2 Resistors in an AC
Circuit
4.3 Inductors in an AC
Circuit
4.4 Capacitors in an AC
Circuit
4.5 The RLC Series Circuit
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4.6 Power in an AC Circuit
4.7 Resonance in a Series
RLC Circuit
4.8 The Transformer and
Power Transmission
4.9 Rectifiers and Filters
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The aim of the course
•
The graduates have to develop a clear understanding of the
basic concepts of electricity and electronics .
•Developing the graduate's skills and creative thought needed to
meet new trends in science.
• Supplying graduates with basic attacks and strategies for
solving problems.
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- Intended Learning Outcomes
A- Knowledge and
Understanding:
B- Intellectual Skills:
1) Concept of electric field, electric flux k electric potential and capacitance.
2) Concept Dc circuits and Ac circuits.
3) Investigate the characteristics of simple series circuits that contain
resistors, inductors, and capacitors and that are driven by a sinusoidal
voltage.
4) Strategies for solving problems related to the previous topics.
1)
2)
C- Professional and
Practical Skills:
1)
2)
3)
D- General and
transferable Skills
1)
2)
3)
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Utilizations of theories, rules and basic sciences to interpret physical
events.
Collecting information from its relevant sources and use it in discussion.
Being able to solve problem sheets related to the material course.
Collect and record data and information from libraries and summarize it in
suitable forms.
The student would be able to apply some experiments related to the course
contents.
Graduate should be able to access data and information from the Internet
related to the course subjects.
Graduate should develop self professional, scientific, and personal attitude
towards continuous education.
Graduate should be able to cooperate in teams
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Chapter 1
Electric Charge and Electric Fields
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Electric Charge
Types: Two types of charges
Positive: Lack of electrons
Negative: surplus of electrons
Unit : Coulomb
+ +
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C
- 9
Coulomb`s Law
+
+
K= 8.89 x109Nm2/C2
r
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Coulomb`s Law
(N)
Ɛo- Another constant called permittivity of
vacuum
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Coulomb`s Law
Several Charges
y
+q
1
F
13
F
F
13
+q
2
+q
3
X
F
23
F
23
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Electric Field
Force acting on a unit positive charge at
the point.
q
+++
(N/C)
r
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Electric Field
Force acting on a unit positive charge at
the point.
q
+++
(N/C)
r
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Lines of Force
Point Charge
-
+
positive
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negative
15
Lines of Force
Dipole
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Lines of Force
Two positive charges
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Lines of Force
Charged plane
+q
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-q
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Lines of Force
Two charged plates
-q
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+q
19
More Coulomb’s Law
kq1q 2
F12  2 rˆ12
r12
r̂12 
r12
r12
+q1
r̂12
r12
+q2
F12
r12
Coulomb’s constant:
permittivity of free space:
Charge polarity:
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2
2
N

m
N

m
1
9
k  8.988x109

9.0x10

2
C2
C
4o
2
1
C
o 
 8.85x1012
4k
N  m2
Same sign
Opposite sign
Force is right
Force is Left
Electrostatics
--- Charges must be at rest!
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Superposition of Forces
F0  F10  F20  F30  ....
r10
+Q1
r20
+Q2
r30
+Q3
F30
F20
+Q0
F10
kq 0 q1
kq 0q 2
kq 0q 3
F0  2 rˆ10  2 rˆ20  2 rˆ30  ....
r10
r20
r30
N
 q1

q3
q2
qi
F0  kq0  2 rˆ10  2 rˆ20  2 rˆ30  ....   kq 0  2 rˆi0
r20
r30
i 1 ri0
 r10

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Zero Resultant Force,
Example
 Where is the resultant
force equal to zero?
q1 = 15.0 mC
q2 = 6.0 mC
 The magnitudes of the
individual forces will be
equal
 Directions will be
opposite
 Will result in a quadratic
 Choose the root that gives
the forces in opposite
directions
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Electrical Force with Other
Forces, Example
 The spheres are in
equilibrium
 Since they are separated,
they exert a repulsive
force on each other
 Charges are like charges
 Proceed as usual with
equilibrium problems,
noting one force is an
electrical force
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Electrical Force with Other
Forces, Example cont.
 The free body
diagram includes the
components of the
tension, the electrical
force, and the weight
 Solve for |q|
 You cannot determine
the sign of q, only that
they both have same
sign
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More Field Lines
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Q dq

A dA
Surface Charge Density:

Volume Charge Density:
Q dq
 
V dV
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Superposition of Fields
EP  E1P  E2P  E3P  ....
r10
+q1
E30
E20
r20
+q2
r30
+q3
P
E10
kq 3
kq1
kq 2
E P  2 rˆ10  2 rˆ20  2 rˆ30  ....
r10
r20
r30
N
 q1

q3
q2
qi
E P  k  2 rˆ10  2 rˆ20  2 rˆ30  ....   k  2 rˆi0
r20
r30
i 1 ri0
 r10

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Superposition Example
 Find the electric field due
to q1, E1
 Find the electric field due
to q2, E2
 E = E1 + E2
 Remember, the fields add
as vectors
 The direction of the
individual fields is the
direction of the force on a
positive test charge
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Electric potential,
 Potential difference in uniform electric field.
 Electric potential point charge.
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Electric Potential Energy
 Electrical potential energy is the energy contained in a
configuration of charges. Like all potential energies,
when it goes up the configuration is less stable; when
it goes down, the configuration is more stable.
 The unit is the Joule.
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Potential difference and electric
potential
 The potential difference ∆V = VB - VA between two
points A and B in an electric field is defined as the
change in potential energy of the system when a test
charge is moved between the points divided by the test
charge qo:
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 The electric potential is a measure of potential
energy per unit charge, the SI unit of both electric
potential and potential difference is joules per
coulomb, which is defined as a volt (V)
that the SI unit of electric field (N/C) can also be expressed
in volts per meter:
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Electric Field and Electric Potential
E=-V/d
Two things about E and V:
 The electric field points in the direction of decreasing
electric potential.
 The electric field is always perpendicular to the
equipotential surface.
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Summary
 Coulomb’s law states that the electric force exerted by a charge q1 on a
second charge q2 is
 The electric field E at some point in space is defined as the electric
force Fe that acts on a small positive test charge placed at that point
divided by the magnitude q0 of the test charge:
The potential difference ∆V = VB - VA between two points A and B in an electric
field is defined as the change in potential energy of the system when a test
charge is moved between the points divided by the test charge qo:
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Sample Problem
Draw field lines for the charge configuration below. The field is 600
V/m, and the plates are 2 m apart. Label each plate with its proper
potential, and draw and label 3 equipotential surfaces between the
plates. You may ignore edge effects.
- - - - - -- - -- - -- - -- - -- - -- - -- - -- - -- - -- - -
++++++++++++++++++++++++++++++++
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