Electrostatics How can an object get charged and

Electrostatics How can an object get charged and how does a charged object affect 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 insulators & conductors? � What are the (names &) methods of charging? � 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? � Being charged means having an excess or shortage of _____ � Which charges move to charge an object? � Why do they move?

Grounding (UN-CHARGING) � This term is used for the process that “uncharges” 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

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

Questions From Demos � What happens when fur is rubbed on the rubber wand? Cloth on the glass wand? � What happens when the wand is brought near a metal bar or gray sphere? Why? � What happens when the wand touches the metal bar or gray sphere, and then is held near? Why? � What happens when the two gray spheres that have been touched by the same wand are brought near each other? Why? � What happens when the two gray spheres that have been touched by different wands are brought near each other? Why? � What happens if someone touches the metal bar or spheres after they have been touched by a wand?

Charging an Object � Charging by : ◦ Friction � 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.

Charging Investigation 1. Use the negatively charged wand to charge the electroscope by CONDUCTION (needs contact). Remove the wand, then bring it back near scope. ◦ You observe: ◦ Charge the glass with the cloth. Bring it near the charged scope. You observe: 2. Ground scope. Use the negatively charged wand to charge the electroscope by INDUCTION (no contact with charged wand, but a ground must be connected and disconnected at the appropriate time. Remove the wand, then bring it back near scope. ◦ You observe: ◦ Charge the glass with the cloth. Bring it near the charged scope. You observe: 3. Record the four steps to charging the scope by induction. Do you know what goes in in each of the four steps? These are found in Lesson 2 b on PCR

Quantity of Charge � The SI unit for charge is the COULOMB (C) � The charge of one electron is -1. 6 x 10 -19 C � The charge of one proton is +1. 6 x 10 -19 C � The quantity of charge equal to 1. 6 x 10 -19 C 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

https: //www. youtube. com/watch? v =nwnj. YERS 66 U

Quantity of Charge � 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 *e = 1. 602 x 10 -19 C * The mass of an electron was also determined to be 9. 11 x 10 -31 kg

Example: Quantity of charge � If sphere on a Van. De. Graaf generator is charged to 10, 000 volts, it has had 1. 74 x 1012 electrons moved off of it. What is the charge of the sphere (sign and number)?

Behavior of Charge and “Charged” Objects � Opposite charges attract and like charges repel � Charged objects can attract neutral objects, by polarizing the neutral objects. Conductors are easy to polarize, insulators are not easy to polarize. � Electrons � The are the only charges to get transferred force between charged objects can be mathematically described by Coulomb’s Law

Questions from the assignment last night?

Assignment � Review 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) Quest: Electrostatics

Electrostatics Day 3 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 INDUCTION. Remove the wand, then bring it back near scope. ◦ You observe: ◦ Charge the glass with the cloth. Bring it near the charged scope. You observe: 3. Check the four steps to charging the scope by induction. Do you know what goes in in each of the four steps?

Electric Force: What factors affect the size and direction of the electric Force on an object? � But wait, what IS force? � When � What does an electric force occur? 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 affects the size and direction of the electric force one charged “particle” exerts on another charged “particle”? � What is the mathematical relationship between electric force (in newtons) and the: � quantity of charge A (in coulombs)? � quantity of charge B (in coulombs)? � distance (in meters) between charges A & B?

What is the mathematical relationship between: � |Fe|(N) and QA(C)? (What if you double, triple, … QA) � |Fe|(N) and QB (C)? (What if you double, triple, … QB) � |Fe|(N) and d (m)? ◦ Fe is electric force ◦ d is distance between the electric charges � Use the Gizmo simulation: Coulomb Force Google Username: Password:

Coulomb’s Law � Fe = k(Q 1 Q 2)/d 2 � F e: �k = 9 x 109 (Nm 2/C 2) � d: � Q 1 & Q 2 are:

Ex: What is the force of attraction/repulsion between an electron and a proton in a hydrogen atom? They are 53 pm (5. 3 x 10 -11 m) 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 �A Fe=EQ 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. 40 m 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: a) 0. 80 from the center? b) 1. 20 m from the center? c) 0. 20 m 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 4 C, and complete the CYU questions � Complete � Play WS on Electric Fields Electric Field Hockey ◦ Google Phet, go to play with sims, Physics, electricity

Coulomb’s Law Problem � If the electrons from one gram of hydrogen were placed in a container and taken to the South Pole, and the protons from the same gram of hydrogen were placed in a container and taken to the North Pole, How much force would these two containers exert on each other?