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

Tests 30% Exam 1, Feb. 15 10%

Exam 2, Mar. 24 10%

Exam 3, Apr. 14 10%

Labs 15% You must pass lab to pass

class! You must complete every

lab to pass lab!

Other 25% Homework Reading Quizzes

Participation 10%

Final Exam 20% 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.

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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

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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

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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.

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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

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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

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

Charge Conservation

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

•  Triboelectric series – Decreasing tendency to lose

electrons

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 q1q2r2

€

Fe =14πε0

q1q2r2

(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 q1q2r2

€

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 q1q2r2

+k q1q3r2

+k q2q3r2

The Electric Field We 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 µC charge?