ELECTROSTATICS  Branch of Physics which deals with the phenomena associated with charges at rest.  Static electricity has always been a part of our daily experience, although we are not aware of it  We feel a very mild electric shock across a carpet and reach out for the doorknob or any metallic object  We see the so-called “fly away hair effect” when we comb our hair several times  Using the same comb, we can also attract small pieces of paper

Electrostatics Electric Charge – an intrinsic attribute of matter (as basic as mass)  can be understood by observing its properties and behavior  can either be “positive” or “negative”  the interaction of these charges can be summarized briefly as: “Like charges repel each other while unlike charges attract each other.”

Electrostatics Benjamin Franklin  Introduced the terms “positive” and “negative” charges  Discovery of the electrical nature of lightning  A statesman, very instrumental in drafting the Declaration of the Independence of the USA  His picture appears in the 100 US Dollar bill  His popular quotation is “Early to bed, early to rise makes a man healthy, wealthy and wise.”

Electrostatics  The modern theory of electric charges is the electron theory  It explains the existence of charges by the structure of an atom  An atom may gain or lose electrons under some circumstances  If it gains electrons, it becomes positively charged; if it loses electrons it becomes negatively charged  The SI unit of charge is the coulomb, abbreviated as C

Electrostatics  Two Laws governing electric charges in nature:  Principle of Conservation of charge  “The algebraic sum of all electric charges in any closed system is constant.”  In any charging process, charges are not created nor destroyed but is merely transferred from body to another.  Quantization of Electric Charge “ The magnitude of the charge of the electron (denoted by the symbol e) is a natural unit of charge.” Every observable amount of electric charge in nature is always an integer multiple of e.

Electrostatics  Important Facts About Proton, Neutron and Electron  The value 1.6 x C is usually designated by a letter e. Thus, an electron has a charge of –e while a proton has a charge of +e. LocationMassCharge ProtonInside the nucleus x kg+ 1.6 x C NeutronInside the nucleus x kgNone ElectronAround the nucleus x kg- 1.6 x C

Methods of Charging  Charging by Friction/Rubbing  Letting a neutral material be in contact with an excessively charged material  Triboelectric series – ranking of some common materials based on their ability to hold or give up electrons  In general, when two different materials are rubbed together, the one that is higher in the list will become positively charged.

Triboelectric Series  Dry hands  Leather  Glass  Human hair  Nylon  Wool  Fur  Silk  Wood  Amber  Rubber  Polyester  Styrofoam  Polyurethane  Polyvinylchloride  Teflon On page 6… Which will be positively charged and which will be negatively charged when the materials in the pair are rubbed against each other? a. human hair and rubber b. amber and wool c. PVC pipe and nylon d. leather and styrofoam

Methods of Charging  Conduction  Charging by contact between the neutral body and the charging body  It should be noted that whenever a neutral body is charged by conduction, the sign of the charge produce is the same as that of the charging body.

Methods of Charging  Charging by Induction  Does not involve contact between the neutral body and the charging body  The neutral body is just brought very near the charging body  In induction, the acquired charge is opposite that of the charging body

Charging by Induction

Coluomb’s Law  The magnitude of force that a particle exerts on another particle is directly proportional to the product of their charges and inversely proportional to the square of the distance between them. where:  F is the force between the two particles, q 1 is the net charge on particle A, q 2 is the net charge on particle B, d is the distance between the particles, k is a proportionality constant which is 9.0 * 10 9 Nm 2 /C 2.  The direction of the force is on the line from one particle to the other.