Transcript Electrostatics_Notes

Electrostatics
Electricity at rest
Electrostatics
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Electrical forces arise from particles in
atoms
Electrons are attracted to protons and
repel other electrons
Attraction and repulsion is attributed
to charge
Like charges repel; opposite charges
attract
Conservation of Charge
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Electrons are neither created nor
destroyed. They are only transferred
between materials, therefore charge is
conserved.
Conservation of Charge
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Positive ions have a net positive
charge  more protons than electrons
Negative ions have a net negative
charge  more electrons than protons
An object that has unequal numbers of
electrons and protons is electrically
charged
Coulomb’s Law
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F = k q1 * q2
d2
k= 9 * 109 Nm2/C2
d= distance
q1 and q2 = charges
Materials
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Conductors  materials which have
loose electrons, like metals
 allow for the motion of electrical
charges
Insulators  materials with tightly
bound electrons, like rubber
 charge is not free to wander
through them
Materials
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Semiconductors  materials that can
be made to behave sometimes like an
insulator and sometimes like a
conductor
Silicon microchips – store a binary
code by turning portions on and off to
charge
Methods of Charging
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Friction  electrons are being
transferred by friction when one
material rubs against another
Contact  electrons are transferred
between materials in direct contact
with each other
Methods of Charging
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Induction  by bringing a charged
object near a conducting surface,
electrons will move in the conducting
surface even without physical contact
By doing this we can redistribute
charge or induce a charge
Grounding  allowing charges to
move off (or onto) a conductor by
touching it
Methods of Charging
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Charging by induction occurs during
thunderstorms when the negatively
charged bottoms of storm clouds
induce a positive charge on the
ground below
Lightning is the electrical discharge
between the clouds and oppositely
charged ground
Charge Polarization
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When a charged material is brought
near an insulator there is no free flow
of electrons between them
But there is a rearrangement in the
orientation or positions of the charges
within the atoms and molecules
themselves
Charge Polarization
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One side of the atom or molecule is
induced to be slightly more positive
(or negative) than the other side
These atoms and molecules have
become electrically polarized
Electric Fields
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Around every electric charge there
extends an aura of energy that
extends through space
This space is filled with an electric field
Electric fields have both magnitude
and direction
Electric Fields
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The direction of an electric field is the
direction that a small positive point
charge would travel if placed in that
field
This charge will move from positive to
negative so all electric fields move
from positive to negative
Electric Fields
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We represent or describe an electric
field using field lines
 lines farther apart signifying
weaker strength
 lines closer together signifying
stronger field strength
Shielding – loops of metal placed
inside an electric field will create a null
zone to the field inside of the loop
Electric Fields
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F=Eq
Force = E-field strength x charge
E= kq
d2