College Physics B - Hadroncrede/FILES/FALL2014/Introduction_Aug...College Physics B Introduction Electric ... • Each week all Mastering Physics problems will be ... • The SI unit

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


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


ElectricForces

Outline

1 Introduction

2 Electric Charge

3 The Scientific Method

4 Electric Forces

CollegePhysics B

Introduction

ElectricCharge


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


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


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


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.

masteringphysics.com/site/login.html


CollegePhysics B

Introduction

ElectricCharge


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


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.

www.iclicker.com/registration

CollegePhysics B

Introduction

ElectricCharge


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


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


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


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:



CollegePhysics B

Introduction

ElectricCharge


ElectricForces

Outline

1 Introduction

2 Electric Charge


4 Electric Forces

CollegePhysics B

Introduction

ElectricCharge


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


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


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


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


ElectricForces

Outline

1 Introduction

2 Electric Charge


4 Electric Forces

CollegePhysics B

Introduction

ElectricCharge


ElectricForces

Scientific Theory and the

Scientific Method

Scientific theories

• must be testable.

• must be continually tested.

CollegePhysics B

Introduction

ElectricCharge


ElectricForces


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


ElectricForces


Scientific Method

Observation leads to theoryexplaining it.

CollegePhysics B

Introduction

ElectricCharge


ElectricForces


Scientific Method


Theory leads to predictionsconsistent with previousobservations.

CollegePhysics B

Introduction

ElectricCharge


ElectricForces


Scientific Method


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


ElectricForces


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


ElectricForces

Outline

1 Introduction

2 Electric Charge


4 Electric Forces

CollegePhysics B

Introduction

ElectricCharge


ElectricForces

Electric Forces

Electric force can be attractive or repulsive.

• It is extremely large.

CollegePhysics B

Introduction

ElectricCharge


ElectricForces

Electric Forces



• Assume two charged particles can be modeledas point particles.

CollegePhysics B

Introduction

ElectricCharge


ElectricForces

Electric Forces



• 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


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


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


ElectricForces

Gravity

“Inverse-Square Law”

CollegePhysics B

Introduction

ElectricCharge


ElectricForces

Gravity

“Inverse-Square Law”

CollegePhysics B

Introduction

ElectricCharge


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

phet.colorado.edu/en/simulation/electric-hockey

CollegePhysics B

Introduction

ElectricCharge


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


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


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.

Documents

College Physics B - Hadroncrede/FILES/FALL2014/Introduction_Aug...College Physics B Introduction Electric ... • Each week all Mastering Physics problems will be ... • The SI unit