Electrostatics How can an object be charged and what affect does that charge have upon other objects in its vicinity?

Essential Questions for Electrostatics What makes up all matter? What does it mean to be “charged”? What is GROUNDING? What are the (names &) methods of charging? What are insulators & conductors? Hey wait, what IS charge? A measurement, a concept….? What do charged objects do? (to other objects)

Electric Charge Matter is made of Neutrons, Protons and Electrons Protons have POSITIVE charge Electrons have NEGATIVE charge Neutrons are uncharged Which has “more” charge? Which charges move to charge an object? Why do they move?

Grounding (UN-CHARGING) This term is used for the process that “un- charges” a charged object. It is performed by contacting a charged object to an object that can give, OR receive ___________ charges, so that the initially charged object is made neutral. It can (partially) happen w/o contact when one object that is highly charged discharges across a gap – that is a spark

Charging an Object Charging by : Friction Conduction Induction Materials rubbed “against” each other transfer … Conduction A charged object is brought in contact with a conductor and there is a transfer of … Induction A charged object is brought NEAR a conductor, the conductor is grounded, there is a transfer of….. the ground is removed, and finally the charged object is moved away from the conductor Polarization (not really charging, as a polarized object’s NET charge can be zero) A charged object is brought near a neutral conductor, electrons on the conductor move (toward, or away from the charged object) and then the polarized object behaves as if it has the ________ charge as the object that caused the polarization.

Conductors and Insulators A good CONDUCTOR allows negative charges to travel around through the material making up the conductor, with very little RESISTANCE. A good INSULATOR makes it very hard for negative charges to travel around through the material making up the insulator. These have a lot of RESISTANCE. A SUPERCONDUCTOR is a material that allows negative charges to flow through it without any RESISTANCE.

Conductors and Insulators

Conductors and Insulators

Quantity of Charge The SI unit for charge is the COULOMB (C) The charge of one electron is -1.6x10-19C The charge of one proton is +1.6x10-19C The quantity of charge equal to 1.6x10-19C is often written as e so the charge of one electron is –e To calculate the charge of a certain number of electrons or protons, use the equation: Q = +ne where Q is quantity of charge, and n is the # of charge carriers

Quantity of Charge Q = +ne To calculate the charge of a certain number of electrons or protons, use the equation: Q = +ne where Q is quantity of charge, and n is the # of charge carriers

Behavior of Charge and “Charged” Objects Opposite charges attract and like charges repel Charged objects can attract neutral objects, by polarizing the neutral objects. Electrons are the only charges to get transferred The force between charged objects can be mathematically described by Coulomb’s Law

Assignment Electroscope Investigation PCR Static Electricity Lessons 1&2 CYU Lesson 1: a(1), b(1-6), c(all), d(1-3), e(1,2,4,5,6) Lesson 2: a(3,4), b(4), c(all), d(all)

Electrostatics Day 2 Warm-up 1. If one million electrons are added to the top of a Van de Graff generator, what is its charge in coulombs? 2. Use the negatively charged wand to charge the electroscope by CONDUCTION. Remove the wand, then bring it back near scope. You observe: 3. Ground scope. Use the negatively charged wand to charge the electroscope by INDUCTION. Remove the wand, then bring it back near scope. Charge the glass with the cloth. Bring it near the charged scope. You observe: 4. Record the four steps to charging the scope by induction. Do you know what goes in in each of the four steps?

Questions from the assignment last night?

Electric Force: What factors affect the size and direction of the electric Force on an object? But wait, what IS force? When does an electric force occur? What factors affect the size and direction of the electric Force on an object?

What affects the size and direction of the electric force one charged “particle” exerts on another charged “particle”?

What is the mathematical relationship between: |Fe|(N) and Q1(C)? |Fe|(N) and Q2 (C)? |Fe|(N) and d (m)? Use the Gizmo simulation: Coulomb Force Go to explorelearning. Username: physics_south Password: Einstein

Coulomb’s Law Fe = k(Q1 Q2)/d2 Fe: k = 9 x 109 (Nm2/C2) d: Q1 & Q2 are:

Ex: What is the force of attraction/repulsion between an electron and a proton in a hydrogen atom? They are 53pm (5.3x10-11m) apart.

Electric Fields The concept of a field is utilized by scientists to explain the surprising force phenomenon that occurs in the absence of physical contact.

Electric Field Defined (mathematically) The electric field is a ratio, comparing the size of the force on a charged object to the size of the charge E=Fe/Q Fe=EQ A slightly charged object in an electric field will experience a small electric force, while a heavily charged object will experience a ____________ force.

Electric Field vs Distance from Charged Object As the distance from a charged object doubles, the electric field ________________ Ex: If a small “test charge” is 0.40m from the center of a charged Van de Graff, it experiences an electric force F. How big is the force when the test charge is: 0.80 from the center? 1.20m from the center? 0.20m from the center?

The Butter Gun

Electric Field Lines (or lines of Force) The field “lines” are really arrows that show the direction of force on a positive “test” charge, and show field strength by how closely the lines are spaced

Electric Field Lines (or lines of Force) Electric Field Lines for Two (different, isolated) Point Charges

Examples of field lines

Assignment: Skim PCR Static electricity 4C, and complete the CYU questions Complete WS on Electric Fields Play Electric Field Hockey Google Phet, go to play with sims, Physics, electricity