Download Electrostatic phenomena

Electrostatic
phenomena
Charge distribution
Electrostatic balance is the condition for
which all the charge located in conductor
are stationary.
The exceeding charge in the conductors is
located on the external surface.
The charge is more concentrated in the
parts of the conductor which are in
electrostatic balance and have a tighter
bending...
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Electric field and electric
potential
Inside a charged balanced conductor the
value of the electric field is null.
On a charged conductor's surface the
electric field direction is perpendicular to
the surface.
The electric potential has the same value at
all points inside and on the surface of a
charged conductor in electrostatic balance.
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The external surface of a charged conductor
in electrostatic balance is always a
equipotential
surface.
Gauss theorem application
The gauss theorem explains why the
exceeding charge is located on the
surface.
Considering a closed surface inside a
conductor:
The electric field is null at all points, so the
electrical flow through the surface is 0.
ɸ=0
The general problem of
electrostatic
It consists in determining the electric
potential, or the electric field at all points of
space.
Once calculated the value of the electric field
at all points of space, we can use Coulomb
theorem.
E = δ/ε
Conductors capacity
Experiments show that the isolated
conductor's charge and potential are
directly proportional.
C = Q/ΔV
C = conductor's capacity
Q = charge on the conductor
The measurement
unit of the capacity
is farad (F):
1 F = 1C/1V
A conductor has the
electrostatic
capacity of 1 F if
electrified with a 1
C charge it reaches
1V of potential.
Spheres in electrostatic
balance
The charges are directly proportional to the
spheres radius. The charge densities are
inversely proportional to the spheres radius.
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This is an example of how the charge
concentrates in the tighter parts of a
conductor: where the bend is tighter (smaller
The condenser
A flat condenser is made by two near parallel metal
sheets called armors.
-Q
+Q
When one of the armors receives a charge Q the
other gains by induction a negative charge -Q. The
Q charge located on the positive armor is directly
Condenser capacity is the division of electric
charge Q and potential difference ΔV
C = Q/ΔV
Outside a infinite plain condenser the electric field is
null.
Inside the electric field is uniform and goes from the
positive armor to the negative armor.
E(plain condenser) = 2E(charge surface) = δ/ε
Condensers in series and
parallel
Equivalent capacity of a condenser network is
the capacity of a single condenser, which has
the same potential difference of the whole
network, that absorbs the same electric
charge.
Parallel condenser
Two or more condensers are linked in parallel if
they are connected so that they have the same
potential difference at their ends.
The equivalent capacity of more condenser
connected in parallel is equal to the sum of the
capacity of every single condenser
Q(parallel) = Q1+Q2
Series condensers
Two or more condensers linked in series carry
on the armors the same charge
Q(series) = Q
The reverse of the equivalent capacity of two or
more series condensers is equal to the sum of
the reverse of their single capacity
Energy stored in a condenser
In all the stages of the electrification the
charges that are already located on the
conductor reject all the other charges that
are added, whereby a work is made.
This is also true if the conductor is a
condenser. And we can apply the formula:
Wc = 1/2QV