Transcript Electrostatics

Electrostatics
Conceptual Physics
Chapter 32-33
Electrostatics
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Definitions
Electrostatics—electricity at rest
Electric field—aura that surrounds
electric charges
Electric current—moving electric
charges
Electrical Forces and
Charges
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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
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Charges in an atom
Conservation of Charge
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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
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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
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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 (q1q2/dSquared)
q = charge, d = distance, k is a constant
coulomb—SI unit of charge
Conductors and
Insulators
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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.
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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
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Friction: stroking a cat’s fur or
scuffing across a rug –one material
rubs against another
Contact—electrons transferred by
touching
Charging by induction
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Induced—charge has been
redistributed because a charged object
is nearby
Induction—charging of an object
without direct contact
Grounding
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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
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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)