Transcript Document

OVERVIEW
• Green sheet
• Online HW assignments
• Practice Problems
• Course overview
See course website
www.physics.sjsu.edu/Becker/physics51
C 2012 J. Becker
GREEN SHEET for PHYSICS 51 Sec. 1
Fall 2009 TTh 1030-1145 Sci-253
ELECTRICITY AND MAGNETISM
Dr. Joseph F. Becker
OFFICE HOURS: SCI-322 TTh 1300-1430
OFFICE PHONE: 408-924-5284; email [email protected] >>subject: “Physics 51”
PHYSICS DEPARTMENT PHONE: 408-924-5210
PHYSICS WALK-IN TUTORING CENTER: SCI-326
COURSE WEBSITE - http://www.physics.sjsu.edu/becker/physics51
th
REQUIRED TEXT: University Physics, 12 Ed., Vol. 2 by Young & Freedman
(Addison-Wesley) AND an online access code to go with the text.
PREREQUISITES: PHYSICS 50 or 70, and MATH 21 or 31
GRADING: 45% Midterm tests (20% and 25%)
30% Comprehensive final exam
10% ONLINE Homework
12% Short quiz, clickers, etc. grades
3% Lab grade
TENTATIVE TEST DATES / SCHEDULE
There will be no make-up tests.
#1 Thursday Sept. 24 Chapters 21A, 25, 26, 21B, 22
#2 Thursday Nov. 5 Chapters 23, 24, 26 RC, 27, 28
FINAL EXAM DATE: Monday, Dec. 14 at 0945-1200 in the
regular lecture room. If you have a conflict, discuss this with
your instructors during the second week of class, not later!
Min.
Course
Score Grade
93.0
90.0
87.0
83.0
80.0
77.0
73.0
70.0
67.0
63.0
60.0
A
AB+
B
BC+
C
CD+
D
DF
HOMEWORK: Assignments will not be accepted late. Students doing less than half the
assigned homework correctly will receive an “F” for the course.
There will be weekly assignments submitted online.
Students are required to register online to access the homework/tutoring website and to do
homework online. For this you will need: 1) Your personal access code, 2) the course ID which
is BECKER511F09, 3) a valid email address. There are several ways to get an access code.
You can buy a new textbook with a package called MasteringPhysics, Student Access Kit. You
can get the access code from another student in a Physics 50, 51, or 52 section that is not using
the code. You can return your textbook and buy a new book which comes with the
MasteringPhysics package. You can purchase an access code online (using a credit card) for
about $50 at http://www.masteringphysics.com: click on the picture of OUR textbook, then click
BUY NOW, and follow the instructions.
PROFICIENCY TESTS: In order to pass this course you must pass three 15-minute proficiency
tests on vector addition, DC circuits, and use of integration to calculate electric or magnetic fields.
PHYSICS 51 LAB: You must pass the Physics 51 lab this semester in order to pass this course.
OVERVIEW: This course covers the fundamental principles of basic dc and ac circuits, electric
and magnetic fields, and electromagnetic waves. This is a problem-solving course that will
provide the student with an excellent background for understanding the foundations of modern
technology and for preparing for more advanced courses in science and engineering.
CONTINUATION OF GREEN SHEET: See course website.
Chapters
I ELECTRIC FIELDS
(TENTATIVE)
CH. 21A Electric Charge and Electric
Field (Basic Concepts)
CH. 25 Current, Resistance, and
Electromotive Force
(The flow of electric charge)
CH. 26 Direct Current Circuits
(Direct, or constant, current flow)
CH. 21B Electric Charge and Electric
Field (Coulomb's Law is used to
calculate the force on electric charges)
CH. 22 Gauss's Law (Used to calculate
the value of the electric field)
CH. 23 Electric Potential (Related to
potential energy of a charge)
CH. 24 Capacitance and Dielectrics and RC Circuits (Energy is stored in
the electric field of a capacitor)
II MAGNETIC FIELDS
CH. 27 Magnetic Field and Magnetic
Forces (Magnetic field exerts a force on
a moving electric charge)
CH. 28 Sources of Magnetic Field
(Ampere's and Biot-Savart’s Laws are
used to calculate the magnetic field)
CH. 29 Electromagnetic Induction
(Faraday's Law - electric generators)
CH. 30 Inductance (Energy is stored in
the magnetic field of an inductor or coil)
CH. 31 Alternating Current (Alternating,
or changing the direction of current)
CH. 32 Electromagnetic Waves
(Maxwell's equations - the basic
equations of electromagnetic theory)
Reading and Practice Problems
Practice Problems are listed below
(see website for ONLINE HW)
Read sections 21.1, 2, 3, 6;
for Lab #2 read sections 21.6 & 23.4;
HW Q21.4; and 21.72
Read sections 25.1 through 25.5
(but omit current density J )
HW Q25.14, Q25.20; and 25.31
Read sections 26.1, 2, 3, 5 (RC later)
HW Q26.3, Q26.4, Q26.7; and 26.21
Read sections 21.4, 5, 6
HW Q21.16, Q21.23; and
21.90 (a and b only)
Read sections 22.1 through 5
HW Q22.5; and 22.42 (a, c, d only)
Read sec. 23.1 through 5
HW Q23.9; and 23.79 (a and b only)
Read sections 24.1 through 4
and (RC circuits) 26.4
HW Q24.7, Q24.15; and 24.15, and
(RC ckts) 26.49 (a, b and c only)
Date
DUE
Read sections 27.1 through 9
HW Q27.15; and 27.15
10-20
(Tue)
Read sec. 28.1 through 7
HW Q28.10; and 28.13, 28.38
10-27
(Tue)
TUES
8-27
(Thu)
9-1
(Tue)
9-8
(Tue)
9-15
(Tue)
……
9-29
(Tue)
10-6
(Tue)
10-13
(Tue)
……
Read sec. 29.1 through 7
HW Q29.7; and 29.23
Read sec. 30.2 through 6
HW Q30.12; and 30.32
Read sec. 31.1 through 6
HW Q31.9, Q31.16; and 31.29
Read sections 32.1, 2, 3
HW Q32.3; and 32.3
11-10
(Tue)
11-24
(Tue)
11-24
(Tue)
11-24
(Tue)
1. Draw carefully labeled coordinate systems and diagrams, write necessary
equations in terms of variables, and show all steps including units.
2. Not all topics in each chapter will be covered, as noted above.
3 slides printed on a page
Chapter 21A Electric Field and
Coulomb’s Law
•
•
•
•
Electric charge
Conductors, insulators,
and induced charge
Coulomb’s Law
Electric field lines
C 2012 J. Becker
(sec. 21.1)
(sec. 21.2)
(sec. 21.3)
(sec. 21.6)
Learning Goals - we will learn:
• The nature of electric charge.
• How objects become electrically charged.
• How to use Coulomb’s Law to calculate the
electric force between charges.
• How to calculate the electric field caused
by electric charges.
• How to use the idea of electric field lines
to visualize electric fields.
Electric charge
•Protons have positive charge
•Electrons have negative charge
•Opposite signs attract
•Similar signs repel
•Electric field – used to calculate force
between charges
C 2012 J. Becker
Photocopiers are amazing devices. They
use electric charge to hold fine dust
(toner) in patterns until the pattern may
be transferred to paper and made
permanent with heat.
LITHIUM (Li) ELEMENT
Atom: electrically neutral 3 protons and 3 elec.
Positive ion: missing one electron so net
charge is positive
Negative ion: has added electron so net
charge is negative
A positive charge and a negative
charge attract each other.
Two positive charges
(or two negative charges)
repel each other.
Figure 21.5
Electric forces in action
Figure 21.1a
Figure 21.1b
Figure 21.1c
Q21.1
When you run a plastic rod with fur, the plastic rod becomes
negatively charged and the fur becomes positively charged.
As a consequence of rubbing the rod with the fur,
A. the rod and fur both gain mass.
B. the rod and fur both lose mass.
C. the rod gains mass and the fur loses mass.
D. the rod loses mass and the fur gains mass.
E. none of the above
Q21.2
When you run a plastic rod with fur, the plastic rod becomes
negatively charged and the fur becomes positively charged.
As a consequence of rubbing the rod with the fur,
A. the rod and fur both gain mass.
B. the rod and fur both lose mass.
C. the rod gains mass and the fur loses mass.
D. the rod loses mass and the fur gains mass.
E. none of the above
Figure 21.6a
Copper is a good conductor of electricity;
Glass and nylon are good insulators
Figure 21.6b
Figure 21.6c
CHARGING A METAL SPHERE BY INDUCTION
Charges are free to move in a conductor but
are tightly bound in an insulator.
The earth (“ground”) is a large conductor
having many free charges.
POLARIZED
insulator
CHARGED COMB ATTRACTS
A PIECE OF PAPER
In an insulator the charges
can move slightly (called
polarization of the insulator).
A piece of paper is attracted
to a charged comb because
the positive charges are
closer to the negatively
charged comb
(in the upper figure).
Q21.3
A positively-charged piece of plastic exerts an attractive force
on an electrically neutral piece of paper. This is because
A. electrons are less massive than atomic nuclei.
B. the electric force between charged particles
decreases with increasing distance.
C. an atomic nucleus occupies only a small part of
the volume of an atom.
D. a typical atom has many electrons but only one
nucleus.
Q21.4
A positively-charged piece of plastic exerts an attractive force
on an electrically neutral piece of paper. This is because
A. electrons are less massive than atomic nuclei.
B. the electric force between charged particles
decreases with increasing distance.
C. an atomic nucleus occupies only a small part of
the volume of an atom.
D. a typical atom has many electrons but only one
nucleus.
An uncharged conductor can attract the
charge imparted to paint droplets. Excess
charges can flow to or from “ground”
Car door
-e
The imaging drum is aluminum coated with
selenium, which changes from an insulator to
a conductor when illuminated with light.
Figure 21.2
LASER PRINTER USES CHARGED TONER
FORCE
between two charges
is given by
Coulomb’s Law:
| F | = k | Q qo | / r 2
We can use our notion of the
gravitational field to form the concept of an
ELECTRIC FIELD (E)
Recall force between two masses: F = m g
g is the gravitational field (9.8 m/sec2)
| F | = G | M m | / r2
The force between two charges Q and qo is
given by: F = qo E
| F | = k | Q qo | / r2
Coulomb’s Law:
| F | = k | Q qo | / r 2
Rearranged:
| F | = | qo [k Q/r2] |
Gives us:
F = qo E
where the electric field
E is:
| E | = | k Q / r2 |
Q21.5
Three point charges lie at the
vertices of an equilateral triangle as
shown. All three charges have the
same magnitude, but Charges #1
and #2 are positive (+q) and Charge
#3 is negative (–q).
The net electric FORCE that
Charges #2 and #3 exert
on Charge #1 is in
Charge #2
+q
Charge #1
+q
y
–q
x
A. the +x-direction.
B. the –x-direction.
C. the +y-direction.
D. the –y-direction.
E. none of the above
Charge #3
Q21.6
Three point charges lie at the
vertices of an equilateral triangle as
shown. All three charges have the
same magnitude, but Charges #1
and #2 are positive (+q) and Charge
#3 is negative (–q).
The net electric FORCE that
Charges #2 and #3 exert
on Charge #1 is in
Charge #2
+q
Charge #1
+q
y
–q
x
A. the +x-direction.
B. the –x-direction.
C. the +y-direction.
D. the –y-direction.
E. none of the above
Charge #3
Q21.7
Three point charges lie at the
vertices of an equilateral triangle as
shown. All three charges have the
same magnitude, but Charge #1 is
positive (+q) and Charges #2 and #3
are negative (–q).
The net electric FORCE that
Charges #2 and #3 exert
on Charge #1 is in
Charge #2
–q
Charge #1
+q
y
–q
x
A. the +x-direction.
B. the –x-direction.
C. the +y-direction.
D. the –y-direction.
E. none of the above
Charge #3
Q21.8
Three point charges lie at the
vertices of an equilateral triangle as
shown. All three charges have the
same magnitude, but Charge #1 is
positive (+q) and Charges #2 and #3
are negative (–q).
The net electric FORCE that
Charges #2 and #3 exert
on Charge #1 is in
Charge #2
–q
Charge #1
+q
y
–q
x
A. the +x-direction.
B. the –x-direction.
C. the +y-direction.
D. the –y-direction.
E. none of the above
Charge #3
ELECTRIC FIELD LINES START AND END
AT ELECTRIC CHARGES
An electric charge is surrounded by an electric
field just as a mass is surrounded by a
gravitational field.
Electric field and equipotential lines
are perpendicular to each other
In Lab #2 a
voltmeter is
used to measure
the equipotential
lines (in Volts)
in order to
determine the
magnitude and
direction of the
electric field
lines.
Q21.9
Two point charges and a point P lie
at the vertices of an equilateral
triangle as shown. Both point
charges have the same magnitude q
but opposite signs. There is nothing
at point P.
The net electric FIELD that Charges
#1 and #2 produce at point P is in
Charge #1
–q
P
y
+q
x
A. the +x-direction.
B. the –x-direction.
C. the +y-direction.
D. the –y-direction.
E. none of the above
Charge #2
Q21.10
Two point charges and a point P lie
at the vertices of an equilateral
triangle as shown. Both point
charges have the same magnitude q
but opposite signs. There is nothing
at point P.
The net electric FIELD that Charges
#1 and #2 produce at point P is in
Charge #1
–q
P
y
+q
x
A. the +x-direction.
B. the –x-direction.
C. the +y-direction.
D. the –y-direction.
E. none of the above
Charge #2
Q21.11
Two point charges and a point P lie
at the vertices of an equilateral
triangle as shown. Both point
charges have the same negative
charge (–q). There is nothing at
point P.
The net electric FIELD that Charges
#1 and #2 produce at point P is in
Charge #1
–q
P
y
–q
x
A. the +x-direction.
B. the –x-direction.
C. the +y-direction.
D. the –y-direction.
E. none of the above
Charge #2
Q21.12
Two point charges and a point P lie
at the vertices of an equilateral
triangle as shown. Both point
charges have the same negative
charge (–q). There is nothing at
point P.
The net electric FIELD that Charges
#1 and #2 produce at point P is in
Charge #1
–q
P
y
–q
x
A. the +x-direction.
B. the –x-direction.
C. the +y-direction.
D. the –y-direction.
E. none of the above
Charge #2
Q21.13
A PROTON (+e) is released from rest in an electric field. At
ANY later time, the velocity of the proton
A. is in the direction of the electric field at the position
of the proton.
B. is directly opposite the direction of the electric field at
the position of the proton.
C. is perpendicular to the direction of the electric field at
the position of the proton.
D. is zero.
E. not enough information given to decide
Q21.14
A PROTON (+e) is released from rest in an electric field. At
ANY later time, the velocity of the proton
A. is in the direction of the electric field at the position
of the proton.
B. is directly opposite the direction of the electric field at
the position of the proton.
C. is perpendicular to the direction of the electric field at
the position of the proton.
D. is zero.
E. not enough information given to decide
Q21.15
The illustration shows the electric
field lines due to three point
charges. The electric field is
strongest
A. where the field lines
are closest together.
B. where the field lines
are farthest apart.
C. where adjacent field
lines are parallel.
D. none of the above
Q21.16
The illustration shows the electric
field lines due to three point
charges. The electric field is
strongest
A. where the field lines
are closest together.
B. where the field lines
are farthest apart.
C. where adjacent field
lines are parallel.
D. none of the above
Forces on electron beam in a TV tube (CRT)
F = Q E and F = m g (vector equations)
TV tube with electron-deflecting charged
plates (orange)
F=QE
Review
see
www.physics.sjsu.edu/Becker/physics51
INTRODUCTION: see Ch. 1
Vectors Review (See Chapter 1)
Used extensively throughout course
C 2012 J. Becker
Vectors are quantities that
have both magnitude and
direction.
An example of a vector
quantity is velocity. A
velocity has both magnitude
(speed) and direction, say
60 miles per hour in a
DIRECTION due west.
(A scalar quantity is
different; it has only
magnitude – mass, time,
temperature, etc.)
A vector may
be composed of
its x- and ycomponents as
shown.
Ax  A cos 
Ay  A sin 
A  Ax  Ay
2
2
2
The scalar (or dot) product of two
vectors is defined as
A  B  AB cos  Ax Bx  Ay By  Az Bz
Note: The dot product of two
vectors is a scalar quantity.
The vector (or cross) product of
two vectors is a vector where the
direction of the vector product is
given by the right-hand rule.
The MAGNITUDE of the vector
product is given by:
A  B  AB sin
Figure 21.14
PROFESSIONAL FORMAT