Transcript Electric Field Lines

ELECTRIC FIELD LINES
Chapter 17-3b
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ELECTRIC FIELD LINES
A convenient aid for visualizing electric
field patterns is to draw lines pointing
in the direction of the electric field
called electric field lines.
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ELECTRIC FIELD LINES
Although these lines do not really exist,
they are useful for analyzing fields by
representing both the strength and
the direction of the field at different
points in space.
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ELECTRIC FIELD LINES
This beneficial because the field of
each point is often the result of more
than one charge.
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ELECTRIC FIELD LINES
Usually, electric field lines are drawn so
that the electric field vector, E, is
tangent to the lines at each point.
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ELECTRIC FIELD LINES
Further the number of lines per unit
area through a surface perpendicular
to the lines is proportional to the
strength of an electrical field of a
given region.
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ELECTRIC FIELD LINES
Thus, E, is stronger where the field
lines are close together and weaker
where they are further apart.
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ELECTRIC FIELD LINES
A positive point charge is represented
by a circle in the middle with rays
pointing outward radially, somewhat
like quills radiate from the body of a
porcupine.
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ELECTRIC FIELD LINES
Because a positive test charge placed
in this field would be repelled by the
positive charge, extending to infinity.
Similarly, the electric field lines for a
negative point charge are directed
inward towards the charge.
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ELECTRIC FIELD LINES
Note that the lines are closer together
as they get near a charge, indicating
that the strength of the field is
increasing.
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ELECTRIC FIELD LINES
The figure shows the electric field lines
for two point charges of equal
magnitudes but opposite signs this is an electric dipole.
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ELECTRIC FIELD LINES
In this case, the number of lines that
begin at the positive charge must equal
the number of lines terminating on the
negative charge.
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ELECTRIC FIELD LINES
The figure shows the electric field lines
in the vicinity of two equal positive
point charges which result in the same
number of lines emerging from each
charge as they are equal in magnitude.
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CONDUCTORS IN ELECTROSTATIC EQUILIBRIUM
A good electric conductor (Cu) contains
charges that are not bound to any atom
and are free to move about within the
material. When no net motion of
charge is occurring within a conductor,
the conductor is said to be in
electrostatic equilibrium.
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CONDUCTORS IN ELECTROSTATIC EQUILIBRIUM
A conductor that is isolated has four
properties:
(1) The electric field is zero everywhere
inside the conductor
(2) Any excess charge on an isolated
conductor resides entirely on the
conductor’s outer surface.
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CONDUCTORS IN ELECTROSTATIC EQUILIBRIUM
(3) The electric field just outside a charged
conductor is perpendicular to the
conductor’s surface
(4) On an irregularly shaped conductor,
charge tends to accumulate where the
radius of curvature of the surface is
smallest (at sharp points)
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VAN DE GRAFF GENERATOR
In nuclear physics research, a Van de
Graaff generator is often used to
generate electric charge.
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VAN DE GRAFF GENERATOR
If protons are introduced into a tube
attached to the dome, the large electric
field of the dome exerts a repulsive
force on the protons causing them to
accelerate to energies high enough
initiate nuclear reactions between the
protons and various target nuclei.
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VAN DE GRAFF GENERATOR
A simple Van de Graaff generator is
shown below. It is designed to avoid
ionizing the air, which would allow
charge to leak off into the atmosphere.
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VAN DE GRAFF GENERATOR
In a Van de Graaff
generator, charge is
transferred to the dome by
a rotating belt that is kept in
motion by a pulley.
The charge is deposited on
the belt and then
transferred to the dome at
the top.
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