Elektrostatika: Hukum Coulomb

Electrostatic:
Electric Potential
{
Chapter 24 Halliday-Resnick 9th Ed.
Potential due to a continuous
charge distribution:
Line of charge
=
= /
=
=
=
=
=
ln
;
=
+
=
+
+
/
+
Potential due to a continuous
charge distribution:
charged disk
=
=
=
=
=
=
=
=
+
+
+
−
Calculating the Field from the Potential
a positive test charge
moves through a
displacement
from one equipotential
surface to the adjacent surface.
the work the electric field does on the test
charge during the move is
=−
=
=
=−
cos
=−
=−
=−
Electric Potential Energy of a System of Point Charges
The electric potential energy of a system of fixed
point charges is equal to the work that must be
done by an external agent to assemble the system,
bringing each charge in from an infinite distance.
=
What is the electric
potential energy of this
system of charges? Assume
that = 2
and that
ql = +3 nC,
q2 = -2 nC
q3 = +5 nC,
Potential of a Charged Isolated
Conductor
−
=−
∙
= 0, inside the conductor
− =0
=
Capacitance
{
Chapter 25 Halliday-Resnick 9th Ed.
Capacitors
{
Capacitor
• Charged : equal magnitudes but
opposite signs: +q and -q.
• charge of a capacitor = q,
• q net charge on the capacitor,
which is zero
• all points on a plate are at the same
electric potential.
• there is a potential difference be
tween the two plates
• The charge q and the potential
difference V for a capacitor are
proportional to each other:
=
, C: capacitance
Capacitance




=
a measure of how much charge must be put
on the plates to produce a certain potential
difference between them:
The greater the capacitance, the more charge
is required.
The SI unit of capacitance : coulomb per volt
(a.k.a. farad [F])
1 farad = 1 F = 1 coulomb per volt = 1 e/v.
Calculating the Capacitance
Electric Field
=
=
∙
=
Potential Difference
−
=−
=+
∙
∙
Parallel plate
capacitor:
so large, so close together
the fringing of the electric
field can be neglected
Potential
Electric Field
=
=
=
→
∙
=
=
−
=+
=
Geometry dependent
Difference
=−
∙
∙
=
Cylindrical
Electric Field
=
=
=
Potential Difference
=+
=−
=
=
∙
ln
ln /
Spherical
Electric Field
=
=
=
Potential Difference
=+
=−
=
=
−
4
=
4
∙
1
−
1
1− /