Electrostatics

Electricity Comes 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 Charges Opposites attract Likes repel Any charged object attracts a neutral object

Law of Conservation of Charge Whenever 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 Charge Charging of a solid results from the transfer of electrons from one material to another Negative charge results when an object acquires an excess of electrons Positive when has deficit

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

Examples When 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 Rubbing Objects charged by rubbing usually lose their charge quickly Charge may be neutralized by ions in the air Charge may “leak” off onto polar molecules like water in the air Why is there more static electricity on dry days?

Insulators and Conductors Solids fall into two main categories as far as electric properties Conductor – allows charge to flow electrons not tightly held so can move freely through the material Insulator – charge cannot flow electrons tightly bound and cannot move

Semiconductor Intermediate between conductor and insulator Few electrons are free Silicon, germanium, carbon

Electroscope Device that detects charges present

Charging by Contact When a charged object touches a conductor, the charges “flow” to the conductor and give it the same charge as the initiating object

Charging by Induction Happens when charged object is brought neat but does not touch a neutral object Only – charge can flow When charged object is brought near a conductor, the – charge in the conductor will either be attracted or repelled by the charged object

Grounding Induced charge can be kept by “grounding” the object induced Ground is a wire running to the earth The earth acts as a big reservoir of charge either absorbing or providing electrons

Sparking Highly charged conductors induce charges in nearby objects Electrons 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