2Units of Chapter 20 Electric Charge Insulators and Conductors Coulomb’s Law
3Structure of Matter All material objects are composed of _____. Atom gain or lose its _______ and become a/an ______.There are ____ types of _____ such as ______ and _______ _____.33
4Structure of atomAn atom consists of a _______ and a vast region of ______ outside the nucleus. ________ are present in the region of space outside the nucleus. They are _________ charged and weakly bound to the atom. _________ are often removed from and added to an atom by normal everyday occurrences.44
5Summary of Subatomic Particles Proton Neutron ElectronIn nucleus In nucleus Outside nucleusTightly Bound Tightly Bound Weakly BoundPositive Charge No Charge Negative ChargeMassive Massive Not very massiveCharged versus Uncharged ParticlesPositively Charged Negatively Charged Unchargedprotons > electrons electrons > protons protons = electrons
6The study of the behavior of stationary charges. ELECTROSTATICS:The study of the behavior of stationary charges.ELECTRIC CHARGEThere are two types of electric charge.(positive and negative)Unlike charges - attractiveLike charges - repulsive
7What will happen? Between positive charged object and neutral object Between negative charged object and neutral object7
8Methods of charging By Friction - two objects are rubbed together By Induction - without touchingBy Conduction - with touchingGrounding (the removal of a charge) - the process of removing the excess charge on an object by another object of substantial size.8
9Electric charge is conserved. CONSERVATION OF ELECTRIC CHARGEThe total electric charge of the universe is a constant:Electric charge is conserved.electric charge cannot be created or destroyed, however, it can be transferred from one object to another.
10Charge is quantity The SI unit of charge is the coulomb (C). Represented by:- the electron is -e,- the proton is +e.e = 1.6 x Cmelectron = 9.11 x kgmproton = x kgmneutron = x kg.
11Insulators and Conductors Conductor: A material whose conduction electrons are free to move throughout. Most metals are conductors.Insulator: A material whose electrons seldom move from atom to atom. Most insulators are non-metals.
12Insulators and Conductors If a conductor carries excess charge, the excess is distributed over the surface of the conductor.
13Check your understanding After a comb is rubbed on a wool, it is able to pick up small pieces of paper. Why does the comb lose that ability after a few minutes?During a lighting storm, what is it about staying inside a car that makes it safe?11
14Electric ForceThe electrical force is a push or pull exerted upon an object as a result of an interaction between electrical charges.the electrical force is a non-contact force.The electrical force is vector quantity12
15COULOMB’S LAWCoulomb’s Law states that two point charges exert a force (F) on one another that is directly proportional to the product of the magnitudes of the charges (q) and inversely proportional to the square of the distance (r) between their centers. The equation is:F = electrostatic force (N)q = charge (C)k = 9x109 N. m2/C2r = separation between charges (m)
16The value of k can also be expressed in terms of the permittivity of free space (εo): 9x109 N. m2/C2k is a proportionality constant (the Coulomb's law constant)The value of this constant is dependent upon the medium that the charged objects are immersed in.If the charged objects are present in water, the value of k can be reduced by as much as a factor of 80.
17Coulomb’s LawThe forces on the two charges are action-reaction forces.
18Coulomb’s LawIf there are multiple point charges, the forces add by superposition.
19Coulomb’s Law example problem Sphere A, with a charge of +6.0 μC, is located near another charged sphere B. It has a charge of – 3.0 μC and is located 4.0 cm to the right of A.What is the force of sphere A on sphere B?
20Coulomb’s Law example problem A third sphere C, with a μC charge, is added to the configuration. If it is located 5 cm directly below sphere B. What is the net force on sphere B?18
22SummaryElectrons have a negative charge, and protons a positive charge, of magnitudeUnit of charge: Coulomb, CCharge is conserved, and quantized in units of eInsulators do not allow electrons to move between atoms; conductors allow conduction electrons to flow freely
23SummaryThe force between electric charges is along the line connecting themLike charges repel, opposites attractCoulomb’s law gives the magnitude of the force:Forces exerted by several charges add as vectors