Transcript The forces between electrical charges have an electrical potential

The forces between
electrical charges have an
electrical potential energy
associated with this force.
The total ME = KE +
gravitational PE +
elastic PE + electric PE.
If a positive charge is moved in
a uniform electric field in the
same direction as the field,
there is a change (decrease)
in the electric potential energy
of that charge.
ΔPEelectric = -qEΔd
It is the difference in
potential that is important.
If we set the initial d to be
zero, then:
PEelectric = -qEd
This is only true for a
uniform field.
“d” is the magnitude of
displacement in the
direction of the electric
field. Perpendicular
motion does not
change the PE.
If there are two charges,
another equation is needed.
PEelectric = kq1q2/r
The reference point is infinity.
The ΔPEelectric is
+ for like charges and
- for unlike charges.
What is the electric
potential energy
between two
electrons that are
two meters apart?
The electrical potential
energy associated with
an electron and proton
-18
is -4.35 x 10 J. What
is the distance between
these two charges?
PEelectric depends on
the charge. A more
practical concept is
electric potential:
PEelectric/q = V.
Electric potential is independent
of charge. The reference point
for electric potential is arbitrary,
only the difference in potential is
important. Therefore:
ΔV = ΔPEelectric/q
The unit is the volt, which is
equal to one joule per coulomb.
As a one coulomb
charge moves
through a potential
difference of one volt
it gains (or loses) one
joule of energy.
Remember:
PEelectric = -qEd and
ΔV = ΔPEelectric/q.
So: ΔV = Δ(-qEd/q)
or ΔV
= -ΔEd
Voltage difference
between a point at
infinity and a point
near a point charge:
ΔV = kq/r
These potentials
are scalars, not
vectors; there is
no direction
involved.
A 5.0 mC point charge is at the
origin, and a point charge of
-2.0 mC is on the x-axis at
(3.0m,0.0m). Find the total
potential difference resulting
from these charges between
a point with coordinates
(0.0m, 4.0m) and a point
infinitely far away.
A battery does work to
move a charge. As a
charge moves through a
12V battery its potential is
raised by 12V. If it is a
1 coulomb charge its
energy is raised by
12 joules.