Presentation on theme: "Electrostatics …the branch of physics that studies the nature of charges that’s not moving."— Presentation transcript:
1 Electrostatics…the branch of physics that studies the nature of charges that’s not moving
2 Static Electricity & Electric Current How are they related?What’s the difference in them?How do they relate do the study of electricity?Where (in our daily lives) do we see examples of their use?Can you measure them? How?
4 ATOM BASICSNeutral atoms contain equal number of positive protons and negative electronsOnly electrons move to create chargesWhen atoms lose electrons they become positively charged ionsLike charges repel and opposite charges attract
5 So…. When an object gains or loses electrons it becomes CHARGED!!!! Charge is a property of particlesThis force of attraction or repulsion between charged particles is called the ELECTRIC FORCEAnd the fact that these + or – particles in matter carry electric charge, this is the basic idea of electricity
6 Unit of ChargeCharge of electron and proton are equal in magnitude and opposite in signSymbol for charge is qSI unit of charge is the Coulomb (C)1C = the charge of 6.25 x 1018 electrons1 C = 6.25 billion billion electrons
7 Conservation of Charge Net charge of an isolated system remains constantWhen we charge something, no e- are created or destroyed, e- are simply transferred
8 Electric Charge is Quantized An electrically charged object has an excess or deficiency of some whole number of electrons (cannot be divided into fractions)Charge is said to be quantized, charge only occurs in discrete amounts
10 How much electrical force? Coulomb’s Lawk = 8.99 x 109 N•m²/C²If answer is negative: attracting forceIf answer is positive: repelling force
11 Practice Problem!Two balloons are charged with an identical quantity and type of charge: nC. They are held apart at a separation distance of 61.7 cm. Determine the magnitude of the electrical force of repulsion between them.Felect = 9.23 x 10-7 N
12 So how can an object get charged? Note: any 2 substances that are rubbed together can potentially become charged.By InductionBy Friction &By Contact
13 FRICTION Can cause charge separation Electrons are stripped from one material and added to the other
14 Walking across wool carpet, leather soled shoes have less desire for electrons than the carpet. Electrons get stolen from the shoe by the carpet. When the positively charged person gets near the metal door he will actually attract charges from the door which jump in the form of a spark.
15 STATIC ELECTRICITYElectric charges that can be confined to an object ORElectricity at rest ORThe presence of electriccharge +/- on the surface ofa material
16 ElectroscopeCan be used to determine whether an object is electrically charged
17 Conductor Material through which electrons move freely Examples: copper wire, copper penny, gold, aluminum foilMetals are good conductors because they have free electrons
18 Insulator Material though which electrons do not move freely Ex. Glass, air, rubber, wood, hair
19 It is easy to put a static charge on a insulator because they stay where they are put
20 GROUNDING Removing a static charge by providing a path to the ground Extra electrons move from negatively charged objects to ground until object is neutralWhen positively charged object is grounded electrons move from the ground to neutralize positively charged objectEarth both accepts and furnishes electrons and remains neutral (symbol)
21 To put a charge on a conductor Isolate itUse an insulator to separate it from the ground
22 Pith balls and electroscopes detect electric charges Pith balls and electroscopes detect electric charges. Both are made of metal to allow electrons to move freely, and both use insulators to isolate the metal parts from the ground.
23 WHAT DO YOU KNOW A material through which electrons move easily is: A. an insulatorB. isolatedC. a conductorD. grounding
24 And…Electrostatic charges are often produced by friction between objects made of materials withA. the same attraction for electronsB. different attraction for electrons
25 What about..Rubber has a greater attraction for electrons than wool. When rubber-soled shoes scuff across wool carpet, electrons are …A. stripped from the carpetB. stripped from the shoesC. createdD. destroyed
26 And..A ___________ can still be statically charged, even though it has been touched, because it is a ______________.A. metal ball; conductorB. metal ball; insulatorC. balloon, conductorD. balloon, insulator
27 InductionTransferring a charge without touchingSide of object closest to charging rod receives a charge opposite that of the rodCharge separation is usually temporary
28 Contact or ConductionIf one of the object is charged & touches something that’s not charged, the 2nd object becomes chargedThis is charge by contact.
29 Conduction Transferring a static charge by touching Object receives a charge that is the same as the charging rodCharge is permanent (if isolated)Does object receive same charge or opposite charge of the object touching it?
30 object ends up similarly charged to the object used to charge it. Charge by conductionobject ends up similarly charged to the object used to charge it.Charge by inductionobject ends up oppositely charged to the object used to charge it.
31 Van de Graff generatorCharge is transferred to a student by what which method of transfer?He receives the _____ charge as the dome.When he steps down, the charge goes through him to the earth. What is this called?Great Explanation:
32 WATER AND PAPERHow can water and paper be attracted to both positive and negative rods?The polar molecules turn so that the side closest to the rod is the opposite charge and attracts.
33 Why does a balloon stick to the wall after being rubbed with your hair? Polar molecules on the wall’s surface are charged by induction
34 LightningWind rubs the surface of the ground & buildings, air molecules pick up electrons from them and carry them to the skyGround becomes positively charged and the bottom of clouds become negatively chargedThe clouds ,mostly consist of water vapor a good conductor, build up charge
35 LightningWhen charges are strong enough to flow through air (an insulator) then it takes the shortest course to get rid of excess charge
36 Field ForceForce that is exerted by one object on another even though there is no physical contactGravity and electric force are 2 examplesElectric forces can be either attractive or repulsiveElectric force is much stronger than gravity
37 Electric FieldSince electric force is an action-at-a-distance force an electric field surrounds every arrangement of chargesHas both magnitude and strengthThe magnitude at any point is the force per unit of chargeE = F/q (Electric field = force ÷ charge)SI unit = N/C (vector quantity)
38 Electric FieldBy convention, a positive test charge (qo) is used to measure the fieldTherefore vector arrows point to center of negatively charged object and point away from center of positively charged ball
39 Electric Field Strength E = Fe = kqqo = kqqo qor² r²Note that electric field is produced by nearby charge and not the TEST chargeIf q is positive, the field is directed outwardIf q is negative, the field is directed inward
40 Electric Field LinesLines that represent both the magnitude and direction of the electric field# of lines is proportional to electric field strengthAlways drawn leaving a positive charge to a negative charge