Chapter 20 Electrical Charge

Electrostatics The study of charge that can be –Collected –Held in one place Charged objects exert forces –Attractive (“unlike” charges attract) –Repulsive (“like” charges repel) –The forces are stronger when the charges are closer together

Charging Separation of electrical charge Charges can be moved around BUT No charge can be created or destroyed Law of Conservation of Electrical Charge

Types of Charge Named by Benjamin Franklin (we use his naming conventions to this day) Negative: when hard rubber or plastic are rubbed with fur, the rubber/plastic become negatively charged Positive: when glass is rubbed with wool, the glass becomes positively charged

Microscopic View of Charge Negative charge is electrons Positive charge is protons An object is “charged” if it has an Excess of electrons deficiency of electrons Protons don’t move, electrons transfer during charging

Conductors and Insulators Conductor: electrons are not bound to individual nuclei Electrons are free to “roam” Insulator: Electrons cannot move easily Charge tends to stay put

Methods of Charging Friction Rubbing two objects together Conduction Touching a charged object to an uncharged object transfers charge Induction Holding a charged object near an uncharged object

Coulomb’s Law Formulated by Charles Coulomb ( ) Relates the electrical force to the distance between objects and quantity of charge An “inverse square” law

K is a constant with the value of 9.0 x 10 9 N m 2 /C 2 q A is the charge on object A measured in Coulombs (C) q B is the charge on object B measured in Coulombs (C) A Coulomb is the charge on 6.25 x electrons or protons 1.60 x C is the charge on an individual electon or proton d is the distance between A & B measured in meters

What is the force on object B?

End Chap 20