Electrostatics
Dec 27, 2015
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
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
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