Electrostatics

ElectricityComes from Greek word elektron which

means “amber” because it was noticed that when amber was rubbed with cloth it attracts dust and leaves

This attraction is now called Static Electricity

An object becomes charged due to rubbing and it posses a net electric charge

Benjamin Franklin noticed two types of charge and called them positive and negative

Fundamental Law of ChargesOpposites attractLikes repelAny charged object attracts a neutral

object

Law of Conservation of ChargeWhenever a certain amount of charge is

produced on one body, an equal amount of opposite charge is produced on another body

Net amount of electric charge produced in any process is zero

Atoms and Electron ChargeCharging of a solid results from the transfer

of electrons from one material to another Negative charge results when an object

acquires an excess of electronsPositive when has deficit

Electrostatic Series gold hold e- tight sulfur brass copper rubber wax silk lead fur wool glass acetate lose e- easily

ExamplesWhen rub plastic or rubber object with fur

electrons are transferred from the fur to the plastic: plastic becomes - and fur +

What happens when glass is rubbed with silk?

Charged By RubbingObjects charged by rubbing usually lose

their charge quicklyCharge may be neutralized by ions in the

airCharge may “leak” off onto polar molecules

like water in the airWhy is there more static electricity on dry

days?

Insulators and ConductorsSolids fall into two main categories as far

as electric propertiesConductor – allows charge to flow electrons not tightly held so can move

freely through the materialInsulator – charge cannot flow

electrons tightly bound and cannot move

SemiconductorIntermediate between conductor and

insulatorFew electrons are freeSilicon, germanium, carbon

ElectroscopeDevice that detects charges present

Charging by ContactWhen a charged object touches a

conductor, the charges “flow” to the conductor and give it the same charge as the initiating object

Charging by InductionHappens when charged object is brought

neat but does not touch a neutral objectOnly – charge can flowWhen charged object is brought near a

conductor, the – charge in the conductor will either be attracted or repelled by the charged object

GroundingInduced charge can be kept by “grounding”

the object inducedGround is a wire running to the earthThe earth acts as a big reservoir of charge

either absorbing or providing electrons

SparkingHighly charged conductors induce

charges in nearby objectsElectrons are strongly attracted to

induced opposite charge even if a gap exists between them

Spark is when electrons jump across the gap

Sparking effect can be magnified by changing the shape of the conductor to a sharp point – this concentrates charge at a point