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CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
College Physics B - PHY2054C
Electric Charges and Forces
08/25/2014
My Office Hours:
Tuesday 10:00 - 12:00 Noon
206 Keen Building
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
College Physics B
Recitation Instructors: Dr. Paul Eugenio (Sec. 1 - 3, HCB)
Dr. Dharshani Bopege (Sec. 4 - 6, UPL)
College Physics
UPL 101: Monday, Wednesday 10:10 - 11:00 AM
Prof. Volker Credé
Office: 206 Keen Building
Office Hours: Tuesday 10:00 - 12:00 Noon
Phone: 644-2423
Email: [email protected]
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Outline
1 Introduction
2 Electric Charge
3 The Scientific Method
4 Electric Forces
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Syllabus
Course WEB Address:
http://www.physics.fsu.edu/undergrads/undergrads_courses.asp
or
Blackboard ➜ http://campus.fsu.edu
Textbook:
Physics:
James S. Walker
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
First Day Attendance
Log on to course website (Blackboard):
http://campus.fsu.edu
Use “First Day Attendance” tab under
“Course Tools” and enter the
passcode ...
Deadline: 8 PM tonight
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Course Organization
Lectures: 101 UPL
Monday & Wednesday 10:10 - 11:00 AM
We’ll use i>clickers for in-class questions.
Homework Assignments (Mastering Physics – MP)
Three Tests, Final Exam (see Syllabus)
Laboratories: Monday - Thursday
Recitations: Friday
Be prepared and participate!
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Mastering Physics
There will be one MP assignment every week.
ASSIGNMENT 1 DUE ON 09/03/2014.
(masteringphysics.com/site/login.html)
• Course Name: College Physics B - Fall 2014
Code: MPCREDE87136
• Assignments are due on Monday morning at 8:00 AM;
usually open from Saturday the week before.
~/PHY2054C/schedule_fall14.html
• The answers can be saved and resumed later.
You have to SUBMIT your answers to receive credit.
• They will be graded automatically upon completion.
• The worst assignment will be omitted.
• Reduced credit by 25 % over each day late.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Recitation Hand-In Assignments
• Each week all Mastering Physics problems will beassigned as hand-in problems.(This week’s “Introduction to ...” problems are exempt.)
➜ It is important that you attempt the problems NOTthat you solve them.
• The hand-in assignments are neatly hand-writtensolutions of the assigned problems showing all ofyour work, including a description of the problemsand the use of proper units.
• Hand-in assignments must be turned in during yourrecitation period.
• You will not receive credit for a missed recitation. Youmay have a valid excuse to miss it, but you still miss it.We will not count the worst two scores.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Audience Response System
Register your transmitter online at:
www.iclicker.com/registration
➜ Use FSU ID as student ID (email address)
Deadline: Sunday, August 31st.
I do expect that you will attend class, read the
text, and ASK QUESTIONS.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Laboratories
The lab is a required component of the course!
• Attend the laboratory section which you are
registered for!
• Labs begin later in the semester in the
week of Monday, September 8th.
• Missing a lab session will automatically
result in a course grade of “F”.
If you miss a lab, attend another lab in the same
week! This is your responsibility.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Course Grading
Your grade is calculated based on
• Homework Assignments 10 %
• In-class questions: i>clickers ∗ 10 %∗ 1 pt for participation, 1 pt for correct answer
(review questions)
∗ 2 pts for participation (general questions)
• Class Mini-Exams 30 %
• Final Exam 25 %
• Laboratories 15 %
• Recitations 10 %
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Some Sensible Advice
• Physics is (mostly) based on understanding, and notmemorizing. We will do all we can to help you, butonly you know if you really understand something ornot! Work in groups and discuss physics problems.
• Test yourself on additional problems!
• When you prepare for the exams, make sure youunderstand and can do all the homework problems.You are strongly encouraged to do extra problems.Again, do not just memorize the solutions.
• Attend all classes and the recitation sessions! Therehappens to be a strong correlation between lectureattendance and student performance.
• TutoringZone will cost you a lot of money!
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
PHY2054C
1 First MP homework Assignment is available.
➜ Check HW deadlines on course website/schedule.
2 No labs this week, first-day attendance is NOT required.
3 Lecture Notes at:
~/PHY2054C/schedule_fall14.html
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Outline
1 Introduction
2 Electric Charge
3 The Scientific Method
4 Electric Forces
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Electric Charge
The phenomena of static electricity can be explained by the
notion that objects can gain (or loose) net electric charges.
• There are two types of electric charges
• labeled positive (+) and negative (−)
• with the following basic properties:
• Like charges of the same sign repel each other.
• Unlike charges of the opposite sign attract each other.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
What is electric charge?
Many experiments have established the following fundamental
characteristics of electric charge:
• Charge is a fundamental property of matter.
• Charge is never created nor destroyed - it is conserved.
• The SI unit of charge is the Coulomb.
• Electron charge: −e = −1.602 × 10−19 C
• Proton charge: e = 1.602 × 10−19 C
• The symbol e is used to denote the magnitude of the
basic charge on an electron or proton.
• Symbols q (or Q) are used to denote charge in general.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
What is electric charge?
Many experiments have established the following fundamental
characteristics of electric charge:
• Charge is a fundamental property of matter.
• Charge is never created nor destroyed - it is conserved.
• The SI unit of charge is the Coulomb.
• Electron charge: −e = −1.602 × 10−19 C
• Proton charge: e = 1.602 × 10−19 C
What holds the atom together?
Almost all atoms have the same
number of electrons and protons. Their
total charge is zero. If not, they are called
ions and are said to be electrostatically
charged.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Question
A plastic comb can gain a net charge by combing hair.A charged comb attracts bits of paper because
A paper always has a net charge similar to that of acomb.
B paper always has a net charge opposite to that ofa comb.
C the charge on the comb polarizes the charges inthe paper.
D paper is an insulator and attracts opposite chargesfrom the surrounding air.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Outline
1 Introduction
2 Electric Charge
3 The Scientific Method
4 Electric Forces
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Scientific Theory and the
Scientific Method
Scientific theories
• must be testable.
• must be continually tested.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Scientific Theory and the
Scientific Method
Scientific theories
• must be testable.
• must be continually tested.
• should be simple.
• should be elegant.
Scientific theories can be proven wrong,
but they can never be proven right with
100 % certainty.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Scientific Theory and the
Scientific Method
Observation leads to theoryexplaining it.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Scientific Theory and the
Scientific Method
Observation leads to theoryexplaining it.
Theory leads to predictionsconsistent with previousobservations.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Scientific Theory and the
Scientific Method
Observation leads to theoryexplaining it.
Theory leads to predictionsconsistent with previousobservations.
Predictions of new phenomenaare observed. If the observationsagree with the predictions, morepredictions can be made. If not,a new theory can be made.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Scientific Theory and the
Scientific Method
VILLAGER #1:If she weighs the same as a duck, she’s made of wood.
BEDEVERE: And therefore?
VILLAGER #2: A witch!
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Outline
1 Introduction
2 Electric Charge
3 The Scientific Method
4 Electric Forces
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Electric Forces
Electric force can be attractive or repulsive.
• It is extremely large.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Electric Forces
Electric force can be attractive or repulsive.
• It is extremely large.
• Assume two charged particles can be modeledas point particles.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Electric Forces
Electric force can be attractive or repulsive.
• It is extremely large.
• The magnitude of the electric force between thetwo particles is given by Coulomb’s Law.
Direction of the force is along theline that connects the 2 charges.
• A repulsive force will give apositive value for F .
• An attractive force will give anegative value for F .
• k = 8.99 × 109 N ·m2/C2
“Coulomb constant”
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Features of Coulomb’s Law
Direction of the force
• The product q1 · q2 determines the sign.
• For like charges, the product is positive➜ The force tends to push the charges farther
apart.
• For unlike charges, the product is negative➜ The charges are attracted to each other.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Features of Coulomb’s Law
Direction of the force
• The product q1 · q2 determines the sign.
• For like charges, the product is positive➜ The force tends to push the charges farther
apart.
• For unlike charges, the product is negative➜ The charges are attracted to each other.
The form of Coulomb’s Law is similar to Newton’s Lawof Universal Gravitation:
F = k q1·q2
r2 F = G m1·m2
r2
r = distance between q1 and q2 or m1 and m2
attractive or repulsive always attractive!
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Gravity
“Inverse-Square Law”
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Gravity
“Inverse-Square Law”
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Coulomb’s Law
Every charged particle in the universe attracts (orrepels) every other charged particle with a forcethat is directly proportional to the product of thecharges of the particles and inversely proportionalto the square of the distance between them.
Electric Field Hockey:
phet.colorado.edu/en/simulation/electric-hockey
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Example: Hydrogen Atom
F = k ·
q proton · q electron
r 2= 8.99 × 109
·
−(1.6 × 10−19)2
(0.53 · 10−10)2N
≈ − 8.2 × 10−8 N
a = F/m ≈ 9.0 × 1022 m/s2
with r = 0.53−10 m.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Example: Helium Nucleus
F = k ·
q proton · q proton
r 2= 8.99 × 109
·
(1.6 × 10−19)2
(10−15)2N
≈ + 230 N
with r = 10−15 m.
CollegePhysics B
Introduction
ElectricCharge
The ScientificMethod
ElectricForces
Size of the Electric Force
Assume you have two boxes each containing 1 g ofelectrons:
• There would be 1.1 × 1027 electrons in each box.
• The force between the two boxes would be about3 × 1026 N with the boxes separated by r = 1 m.
➜ This is almost a million times larger than the forcebetween the Sun and the Earth.