General Physics 1

Welcome to Phys 140!

sites.google.com/site/sienaphys140spring2011/

Textbook

• Physics for Scientists and Engineers, 2nd Edition• By Knight

• Required texts• Volume 4 and Volume 3• Workbooks for these volumes

• We will start with Volume 4

• YOUR TEXTBOOK IS YOUR #1 RESOURCE!!!

• You are expected to come to class having read the assigned chapter.

Course Design and Grading

Tests30%

Exam 1, Feb. 15 10%

Exam 2, Mar. 24 10%

Exam 3, Apr. 14 10%

Labs15%

You must pass lab to pass class!

You must complete every lab to pass lab!

Other 25%

Homework

Reading Quizzes

Participation 10%

Final Exam20%

Uniform exams for all sections

Cumulative

Lab Grading• Lab Write-ups 25%

• Formal Lab Write-up 25%

• Participation 25%

• Lab Practicum 25%

• Lab Write-ups

– Write-up due at the end of lab

– C - lacking , B - adequate; A extra – something we didn’t ask for

• Formal Lab Write-up

– Due the following week; graded and returned for editing

– Average of two grades

• Participation

– Grade in each lab

– C - watching, B - helping; A- doing, explaining, writing

• Lab Practicum– Individual test of lab skills

General Physics Lecture 1 5

Class Time

• Reading Quiz

• 2 minute problems

• Group problems

• Lab-style activities

• SHORT lectures

• Classes will be ACTIVE! They will require you to participate and engage in the problems and activities.

General Physics Lecture 1 6

Preparing for Class

• Assigned Reading– One chapter each class/week

• Go through exercises in each chapter– Answers are provided at the end of the

chapter

• Reading quiz – multiple choice or short answer

General Physics Lecture 1 7

Class Website

• Website will include:– Schedule

• http://sites.google.com/site/sienaphys140spring2011/schedule

– Powerpoint slides for each class– Details on Reading Quiz– Mastering Physics HW Questions and due date– Written HW questions and due date– Lab Schedule and link to lab materials– Info on Bike Generator– Extra Credit Opportunities

• Website will be updated each week – check it often

General Physics Lecture 1 8

Attendance Policy

• Students are expected to attend all classes and are responsible for all material covered in class, even when absent.

• Students should understand that some material discussed in class is not covered in the textbook.

• In-class problems and activities can not be made up.

General Physics Lecture 1 9

Attendance Policy

• Attendance is required.• We realize that some absences are unavoidable, and

you should inform your instructor prior to missing any classes.

• Missing more than 3 classes will decrease your overall grade by a letter grade.

• You will be advised to withdraw from the course if you miss more than 5 classes.

Homework

• Weekly Homework will be listed on the schedule• Mastering Physics Homework is due Saturday by 11:30 pm • Homework to be handed in is due Sunday by 5 pm in the

drop box outside RB 121 (Dr. McColgan’s office) or RB 223 (Dr. Vernizzi’s office)

• Grading• Mastering Physic assignments will be worth 15 points each• Written HW

• 4 points per problem• 2 point for working out the problem• 2 point for presentation

• Exams will be very similar to homework, group problems, and labs

General Physics Lecture 1 11

Grading Homework – 4 point scale

• Working out problem– 2: good effort with correct results and reasoning– 1: Incorrect results or reasoning– 0: a very poor effort or no effort

• Presentation– Adequate diagrams– Explanations of model– Units and vector notation– Algebra first (with symbols only), plug in numbers at the end

• Grading– 2: great presentation– 1: presentation problems– 0: extremely poor presentation

General Physics Lecture 1 12

Guidelines for working homework problems

• Given: •  • Find: •  • •Draw a picture!• •Write in pencil• •Clearly label units• •Cancel units when appropriate• •WRITE NEATLY• •Keep work in one column• •Box answers

Extra Credit

• Opportunities announced throughout the semester

• Examples• Assignments• Brown bag lunches• Comics

MATLAB

• MATLAB is widely used in engineering, science and mathematics– Knowledge of MATLAB is a marketable skill

• Physics Department has adopted MATLAB as its official language– You will see it in higher level courses

• We will use it this semester in class and in lab– Data analysis and plotting

– Vector analysis

– Improve understanding abstract concepts such as vector fields

Nature of charge

• Amber is a natural substance that can be naturally charged

• Few naturally occurring objects can be electrically charged

• Static electricity is easily shown with plastic, rubber, and synthetic fibers

• Electrical charges behave like positive and negative numbers

Electrostatics

• Complete the tutorial on electrostatics (both sides of handout)

• Tape activity • http://www.sos.siena.edu/%7Erfinn/phys140s09/tape.pdf

Charge Conservation

• The total charge of an isolated system is conserved.– Rubbing a balloon on hair

• Triboelectric series– Decreasing tendency to lose

electrons

+

No charge

-

Atoms and Electricity

• An atom consists of a very small and dense nucleus    surrounded by much less massive orbiting electrons.

• The nucleus is a composite structure consisting of    protons, positively charged particles, and neutral neutrons.

• The atom is held together by the attractive electric force    between the positive nucleus and the negative electrons.

• Electrons and protons have charges of opposite sign but    exactly equal magnitude.

• This atomic-level unit of charge, called the fundamental    unit of charge, is represented by the symbol e.

Charge quantization

• Where Np and Ne are the number of protons and electrons    contained in the object.• The process of removing an electron from the electron    cloud of an atom is called ionization. • An atom that is missing an electron is called a positive    ion. Its net charge is q = +e.

• A macroscopic object has net charge

Insulators and Conductors• In metals, the outer atomic electrons are only weakly bound to the nuclei.• These outer electrons become detached from their parent nuclei and are free to wander    about through the entire metal. • The metal as a whole remains electrically neutral, but the electrons are now like a    negatively charged liquid.•The electrons in the insulator are all tightly bound to the positive nuclei and not free to    move around.

• Charging an insulator by friction leaves patches of molecular ions on the surface, but these patches are immobile.•    

Illustrations of Coulomb’s Law

• Electroscope

induction conduction

Polarization Force

The Electric Dipole

Coulomb’s Law - magnitude

• K = 9.0 x 109 N m2/C2 – Coulomb’s contant

• q1, q2 = charges– measured in Coulombs (C)– 1 C is a lot of charge!

• r = distance between q1 and q2

€

Fe =K q1q2

r2

€

Fe =1

4πε0

q1q2

r2

(more relevant to future chapters)

ε0 =permittivity of free space

Electric Force

• Similar form as gravitational force (weird, huh?), except– positive and negative charges

• Like charges repel; opposite charge attract

€

Fe =K q1q2

r2

€

Fg =Gm1m2

r2

Net Force from Multiple Charges

• An electrostatic force exists between each pair of charges according to Coulomb’s law

• Add components of forces to get net force when adding multiple charges

€

Fe = Fe,12 + Fe,13 + Fe,23 =k q1q2

r2+

k q1q3

r2+

k q2q3

r2

The Electric FieldWe begin our investigation of electric fields by postulating a field model that describes how charges interact:1.Some charges, which we will call the source charges,    alter the space around them by creating an electric field.2.A separate charge in the electric field experiences a force    exerted by the field.Suppose probe charge q experiences an electric force Fon q due to other charges.

The units of the electric field are N/C. The magnitude E of the electric field is called the electric field strength.

The Electric Field

Group Problems

EXAMPLE 26.6 Lifting a glass bead

EXAMPLE 26.8 The electric field of a proton

Group Problems

Q1

Q4 Q3

Q2

2. Find net force on Q1

+y

+x

1. What is the net force on the 48 C charge?