Transcript Electric potential

Electric potential
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point charge q in electric field “feels” force due to
electric field
moving the charge against this force needs work:
W = - F x = -q  x
(the “-” sign is there because the force exerted to
move the charge must be opposite to the force due
to the electric field)
 the charge gains “electrical potential energy”
by an amount equal to W, the work done moving
the charge
the electrical potential energy per unit charge is
called “(electric) potential”:
electric potential =
electrical potential energy/charge
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a value of the electric (also called electrostatic)
potential V is associated with every point in space;
it is a scalar quantity (i.e. a positive or negative
number), while the electric field is a vector
quantity.
from the electric potential, the electric field can
be derived: it is given by (-) the “steepness of
decrease” of V when one moves in the direction of
its steepest descent:  = -V/ s;
Voltage
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the direction of  is in the direction of
steepest descent of V; V is the change of V
when moving by a distance s in the direction
of steepest decrease;
the potential difference between two points
A, B in the field equals the work done against
the field moving a unit positive test charge
from point A to point B:
VAB = VB - VA = W(AB)/qo
the work done can be positive, negative, or
zero.
only potential (voltage) differences are
important - not the absolute potential values;
electric potential is defined with respect to
some arbitrarily chosen zero-point - there is
no “absolute zero of potential”
usually (but not always): potential is defined in
such a way that it is zero at infinity.
potential (difference) is also called “voltage”
unit of potential or voltage = Volt = J/C
unit of electric field = V/m
(Note: in this section, “” stands for the
electric field, not for energy!)