Chapter 32 Electrostatics - MillerSTEM

Chapter 32Electrostatics

ElectrostaticsElectricity – comes from the Greek word“elektron” meaning “amber”Static Electricity - “the amber effect” wherea rubber rod, glass, or plastic rod rubbedwith a cloth attracts small pieces of paperor dust.

32.1 Electrical Forces and ChargesElectrical forces- a force thatone charge exerts on another.When the charges are thesame sign, they repel; whenthe charges are opposite, theyattract.

32.1 Electrical Forces and ChargesElectrons are negatively chargedProtons are positively chargedNeutrons have no charge.

32.1 Electrical Forces and ChargesCharge on the electron:

32.1 Electrical Forces and ChargesBohr model of the atom

32.1 Electrical Forces and ChargesFour Facts about the Atom1. Every atom has a positivelycharged nucleus surrounded bynegatively charged electrons.

32.1 Electrical Forces and ChargesFour Facts about the Atom2. All electrons are identical; that is,each has the same mass and thesame quantity of negative charge asevery other electron.

32.1 Electrical Forces and ChargesFour Facts about the Atom3. The nucleus is composed ofprotons and neutrons. All protonsare identical. Protons have a massthat is 2000 times the mass of anelectron, but its positive charge isequal in magnitude to the charge ofan electron.

32.1 Electrical Forces and ChargesFour Facts about the Atom4. Atoms usually have the samenumber of protons and electrons, nothe atom has a zero net charge.

32.1 Electrical Forces and ChargesLike charge repel;opposite chargesattract.

32.1 Electrical Forces and ChargesTime for a Gizmo!

32.2 Conservation of ChargeObjects can be charged by rubbing

32.2 Conservation ofChargeCharge comes in twotypes, positive andnegative; like chargesrepel and oppositecharges attract

32.2 Conservation of ChargeLaw of conservation of electriccharge – the principle that the netelectric charge is neither creatednor destroyed but is transferablefrom one material to another.

32.2 Conservation of ChargeAtom is electrically neutral.Rubbing charges objects by moving electronsfrom one to the other.

32.2 Conservation of ChargeAn object that has unequalnumbers of electrons and protonsis electrically charged. If it hasmore electrons than protons, theobject is negatively charged. If ithas fewer electrons than protons,then it is positively charged.

32.3 Coulomb’s LawExperiment shows that the electric forcebetween two charges is proportional to theproduct of the charges and inverselyproportional to the distance between them.

32.3 Coulomb’s LawCoulomb’s law:F kQ1Q 2d2(16-1)F electrical force (Newtons)k constant 9 x 109 Nm2/C2Q1 charge of one particle (Coulombs)Q2 charge of other particle (Coulombs)d distance between charges (meters)

32.3 Coulomb’s LawThe force is along the line connecting thecharges, and is attractive if the charges areopposite, and repulsive if they are the same.

32.4 Insulators and ConductorsConductor:Insulator:Charge flows freelyAlmost no charge flowsMetalsMost other materialsSome materials are semiconductors.

32.4 Insulators and ConductorsIn conductors the electrons are free to movearound and are not anchored to any particularnuclei.This reason is also why electrical conductorsare good conductors of heat- the electrons areloose.

32.4 Insulators and ConductorsIn insulators the electrons are tightly boundand remain with particular atoms.This reason is also why electrical insulatorsare poor conductors of heat- the electrons areconfined.

32.4 Insulators and ConductorsTime for a Gizmo!

32.5 Charging by Friction and ContactObjects can be charged by rubbing

32.5 Charging by Friction and ContactMetal objects can be charged by conduction:Having direct contact with one another

32.6 Charging by InductionThey can also be charged by induction: Nodirect contact with one another

32.6 Charging by InductionAnother way to charge by induction:

32.6 Charging by InductionCharging by induction occurs duringthunderstorms.Lightning is an electrical dischargebetween oppositely charged parts ofclouds.Lightning rods allow the shortest path tothe ground by collecting electrons fromthe air.

32.6 Charging by InductionThe electroscopecan be used fordetecting charge:

32.6 Charging by Induction1. Charge by Conduction(touching)2. Charge by Induction(no touching)

32.6 Charging by InductionTime for a Gizmo!

32.7 Charge PolarizationNonconductors won’t become charged byconduction or induction, but will experiencecharge separation:

32.7 Charge PolarizationPolar molecule: neutral overall, but charge notevenly distributed

Chapter 32 Electrostatics. Electrostatics . with a cloth attracts small pieces of paper or dust. 32.1 Electrical Forces and Charges Electrical forces- a force that one charge exerts on another. When the charges are the same sign, they repel; when the charges are opposite, they attract.