Transcript Electrostatics
Electrostatics
Conceptual Physics Chapter 32-33
Electrostatics
Definitions Electrostatics—electricity at rest Electric field—aura that surrounds electric charges Electric current—moving electric charges
Electrical Forces and Charges
A pair of forces that attract and repel to balance each other that are stronger than gravity Arise from particles in atoms Behavior is attributed to a property called charge Like charges repel; opposite chares attract
Electrical Charges
Charges in an atom
Conservation of Charge
Electrons have a negative charge Protons have a positive charge Neutrons have no charge An atom is neutral There are as many electrons as protons Ion = charged atom
Conservation of Charge
Charge can be created, but equal amounts of positive and neg. balance When you rub a rubber rod against fur the rubber rod will gather the loose electrons from the fur—no new electrons are created or destroyed Electrons cannot be divided—they must be whole Ex: charge of -1 or -2
Coulomb’s Law
Charged particles: the force between the charges varies directly as the product of the charges and inversely as the square of the distance between them F =k (q 1 q 2 /d Squared ) q = charge, d = distance, k is a constant coulomb—SI unit of charge
Conductors and Insulators
Electrons move easily in some materials than in others Conductors-electrons are free to move Insulators—electrons are not free— generally poor conductors Classified as how tightly the atoms of the substance hold their electrons
Conductors cont.
Semiconductors—sometimes act as insulators and sometimes as conductors Ex. Transistors use semiconductors Superconductors—at near absolute zero—certain metals acquire infinite conductivity—zero resistance to flow of charge
Charging by Friction and contact
Friction: stroking a cat’s fur or scuffing across a rug –one material rubs against another Contact—electrons transferred by touching
Charging by induction
Induced—charge has been redistributed because a charged object is nearby Induction—charging of an object without direct contact
Grounding
Charges move off or onto a conductor by connecting it to the ground (Earth) The Earth has so many charges of both types that it accepts or sends as many charges as needed.
Charge polarization
In an insulator there are no free electrons to migrate-instead there is a rearrangement of charged particles Induction occurs when charges are separated by bringing another charge near (WITHOUT touching)