Presentation on theme: "Semester 2: Unit 1 Electrostatics Spring 2015. Agenda 1/20/15 Welcome! Seating Chart Seating Chart Name Game Name Game Info Sheets Info Sheets Introduction."— Presentation transcript:
Semester 2: Unit 1 Electrostatics Spring 2015
Agenda 1/20/15 Welcome! Seating Chart Seating Chart Name Game Name Game Info Sheets Info Sheets Introduction to Electrostatics Activity What do you know about this stuff? What do you know about this stuff?
Seating Chart Arrange yourselves in alphabetical order ACROSS each ROW. You have 2 minutes GO!!
Agenda 1/21/15Double Period Collect Signed Syllabi Complete Intro to Electrostatics Lab Think about: Think about: What causes charge? What causes charge? In what ways can charge build up? In what ways can charge build up? Discuss findings from activity Notes on types of charging Begin Types of charging lab HW: Complete analysis and conclusion of lab
Let’s talk What are the parts of an atom? Which part moves most easily? Which part moves most easily? What is a conductor? Examples? Examples? What is an insulator? Examples? Examples? Big Question: What makes something a conductor or an insulator? What makes something a conductor or an insulator?
Like Charges & Unlike Charges Charge moves due to motion of electrons Electrons are negatively charged When two materials +, repel When two materials -, repel When one material + and one material -, attract
Charging by Conduction Charging by Conduction Redistribution of charge by direct touching together of two objects Made easier/quicker if both are electrical conductors Originally uncharged material gets same charge concentration as originally charged material if contact between the two exists for a long period of time
Charging by Conduction
Charging by Friction When two initially uncharged materials make contact, the better conductor grabs the electrons from the better insulator In the process, both become charged Substance w/more electrons becomes negative; other becomes positive
Charging by Friction High affinity for electrons (conductors) Low affinity for electrons (Insulators)
Charging by Induction Charge accumulates on originally uncharged material due to a charged material being placed nearby the uncharged material at the same time as a ground is established.
Induction Example: Grounding
Induction Example: Contact
Induction Example: + Charge
Induction by Polarization Polarized: the + and – charges are not evenly distributed in a material (+ pole and – pole) When the charged material is an insulator (non-conducting), polarization occurs in the conductor and the two materials are attracted Cellophane on plastic, balloon on shirt
Induction by Polarization
Agenda 1/22/15 Complete Types of Charging Lab At least 2 Problem Solving Activities At least 2 Problem Solving Activities Show off Physics Skills Show off Physics Skills Lab Exit Slip Forces and Free Body Diagram Intro HW: FBD Practice 1
Agenda 1/23/15 Physics Phriday Discuss Types of Charging Analysis Turn in lab Turn in lab Intro to Free Body Diagrams Practice Practice Coulomb’s Law Lab Netbook activity Netbook activity HW: Complete Coulomb’s Law Lab Analysis
Before we start On a separate sheet of paper: Tell me the 4 types of charging AND Draw an example of each type
Agenda 1/26/15 Complete Coulomb’s Law Lab Graphing Hints Graphing Hints Build Coulomb’s Law Build Coulomb’s Law Practice problems with C.L. HW: Finish Write-Up for C.L. Lab
Graphing Hints Indirect Relationship F = -x Inverse Square F =1/x 2 Inverse Relationship F = 1/x F = x
Agenda 1/27/15 Discuss Coulomb’s Law Lab Determine the flaw in the program Determine the flaw in the program Complete Lab Complete Lab Notes on Coulomb’s Law Practice Problems for CL Practice Problems for CL HW: Finish Write-Up for C.L. Lab
Coulomb’s Law F E = k|q 1 ||q 2 | / r 2 k = Coulomb’s Constant = 9.0 x 10 9 Nm 2 /C 2 q 1 & q 2 : Charges in coulombs (C) r = distance from center of one charge to center of the opposite charge (m) If charges opposite, then attractive If charges like, then repulsive force Equal force upon both objects (Newton’s 3 rd Law)
Opposites Attract, Likes Repel
Inverse Square Law Like with sound intensity, there is an inverse- square relationship between force and distance of separation
Fundamental Charge When an atom ionizes to +1 or -1 in chemistry, how much charge does this represent in coulombs? +1 in chem = 1.60 x C = e 1.60 x C is smallest quantified charge Proton = 1.60 x C, electron = x C Also called elementary charge
Net Charge The net charge equals the (number of extra or deficient electrons) x ( +/ x C) q = Ne If you have a substance with 5 extra electrons, then q = (5) (-1.6 x C) = -8.0 x C
Net Charge What is the net charge in Coulombs of a... Fe atom? Fe 2+ ion? Fe 3+ ion? Charge amounts are always simple whole number multiples of the fundamental charge!
Coulomb’s Law in an Atom What is the average electric force between a proton and an electron in a hydrogen atom? (average distance of separation between p + and e - is 5.3 x m) Answer is 39 orders of magnitude greater than gravitational attraction between the two!
Agenda 1/28/15Doubles Turn in Coulomb’s Law Lab Final Questions Final Questions Lab Exit Slip next period Lab Exit Slip next period Practice Net Charge and CL Practice Problems for CL Practice Problems for CL Practice Net Charge Practice Net Charge Review Everything up to now HW: Study for Quiz Tomorrow
Agenda 1/29/15 Discuss the Review Worksheet Types of Charging Types of Charging Coulomb’s Law Coulomb’s Law Review Activity for types of charging Brief Review Quiz HW: None for tonight
Agenda 1/30/15 Review Electrostatics Quiz Amount of Electrons on a Balloon Lab q = Ne q = Ne More Force Practice…maybe HW: Write up the balloon lab
Agenda 2/4/15 Pass Back A LOT!! Collect Balloon Lab from the rest Electric Field PhETs Field of Dreams and Field Hockey Field of Dreams and Field Hockey Notes of E-Fields and Diagrams Practice Problems Practice Problems HW: Complete E-Field WS
Electric Fields Vector quantity Relates the force exerted on a positive test charge to the size of the test charge Changes with location Unit: N/C E = Coulomb’s force on q’ E = F E q’ q’ q’ q’
Example Problem What is the strength and direction of the electric field 0.250m to the right of a 1.00C electric charge? What is the strength of the field.250m to the left of the same charge?.250m above the same charge?
Electric Field Lines Arrows show the force direction acting upon a positive test charge The more field lines per area, the more intense the electric field is. Notice that arrows flow out of the positive charge.
Electric field lines: Multiple Charges Charges of opposite sign display a watermelon or football- shaped field line structure between them. Again, arrows flow out of + and into -
Electric field lines: Multiple Charges Charges of same sign display a diamond- shaped field line structure between them.
Electric field lines: Multiple Charges Show field lines entering or leaving each charge in the ratio of the relative magnitudes of the charges. Above, red charge (+) has 12 lines leaving, blue charge (-) has 6 lines entering, so red charge must have double the magnitude that the blue charge possesses.
Electric field lines: Multiple Charges More powerful charge tends to dominate the less powerful one and change the basic watermelon/ diamond shape.
Electric Field Lines: Charged Conductors Two oppositely- charged conducting plates have field lines roughly linear between them and rounded off their edges.
Rules Recap for Drawing E- Field Lines 1. Don’t have field lines cross. 2. Have the same ratio of lines entering/exiting charges as the ratio of the magnitude of the charges 3. Have at least 3 lines entering/exiting all charges 4. Best amount of field lines per charge is from 4-12 lines.