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)