Transcript The Electric Field

The Electric Field
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The Electric Field
A region in space around a charged
object in which a stationary charged
object experiences an electric force
because of its charge.
IT’S A FORCE FIELD!
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Electric Field
• An electric field
– is the space that surrounds any charged object.
– is a vector quantity having magnitude and direction.
– has a magnitude at any point that is the force per unit
charge.
– obeys the inverse-square law for a point source.
Electric Field
• Field lines
– are used to visualize an electric field.
– show the direction of an electric field - away
from positive and toward negative.
– show the intensity of an electric field:
• Lines bunched together  field is stronger
• Lines farther apart  field is weaker
Field Lines
• DO NOT REALLY EXIST!
• A useful method for representing the
strength and direction of an electric field at
a point in space.
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Field Lines
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Field Lines
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Field Lines
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Field Lines
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The Electric Field
Electric Field strength is a ratio between the force
on the charged particle and the charge of the
particle
Felectric
E
qo
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The Electric Field
Q
- - - - - - -
qo
E
+
qo is a “test charge” (proton)
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The Electric Field
Q
+ + +
+ +
+ + +
+
+ +
qo
E
+
qo is a “test charge” (proton)
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The Electric Field
Electric Field strength depends on charge and
distance.
The closer that qo gets to Q, the stronger the force
between them
Oh yeah, field strength is a VECTOR quantity!
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The strength of an electric field is measured by
the force
1
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ve
.
1
al
lo
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ab
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a.
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ly
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ex
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A. exerted on a charge in
the field.
B. between electric field
lines.
C. between oppositely
charged parallel
plates.
D. all of the above.
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The direction of an electric field, by convention,
is the direction of force that the field would exert
on
1
ve
lo
ft
he
at
ab
o
om
n.
pr
ot
o
a
1
.
1
al
an
el
ec
tro
n.
1
an
A. an electron.
B. a proton.
C. an atom.
D. all of the above
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Electric Potential
• Electric potential energy is the energy
possessed by a charged particle or other
object due to its location.
• If a particle is released, it accelerates away
from the sphere, and its electric PE changes
to KE.
Electric Potential
• Batteries and generators pull negative
charges away from positive ones, doing
work to overcome electrical attraction.
• The amount of work done depends on the
number of charges and the separation
distance.
• Work done by the battery and generator
becomes available to a circuit as electric
potential energy.
Electric Potential
• Electric potential energy per charge
• Energy that a source provides to each unit
of charge
electric potential energy
Electric potential =
charge
Electric Potential
• Electric potential and voltage are one and
the same.
• The unit of measurement is the volt.
1 Volt =
1 Joule
1 Coulomb
Voltage Sources
• A potential difference exists when the ends of an
electrical conductor are at different electric
potentials.
• Batteries and generators are common voltage
sources.
• Charges in a conductor tend to flow from the
higher potential to the lower potential.
• The flow of charges persists until both ends reach
the same potential. Without a potential difference,
no flow of charge will occur.
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Electric potential energy (like all forms of
energy) is measured in joules. Electric potential
(electric potential energy per charge), on the
other hand, is measured
1
in
o
als
am
w
pe
r
jo
ul
e
es
.
s.
1
at
ts
.
1
in
in
vo
lt s
.
1
in
A. in volts.
B. in watts.
C. in amperes.
D. also in joules.
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When you do work on an electrically charged
particle, you change the particle's
er
po
w
ac
it a
nc
e
rg
y.
t ia
le
ne
rg
e
po
te
n
1
.
1
.
1
.
1
ca
p
charge.
potential energy.
capacitance.
power.
ch
a
A.
B.
C.
D.
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When you increase the potential energy of a
charged particle, you increase its ability to
he
at
.
to
ns
fo
rm
ar
t ic
rp
ot
he
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ch
ar
tra
lse
ge
hi
n
et
so
m
on
or
k
1
do
w
1
t.
1
le
s.
1
co
nd
uc
A. do work on
something else
B. charge other
particles.
C. conduct.
D. transform to heat.
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Electric potential, measured in volts, is a ratio of
nt
.
rre
ge
.
cu
er
to
to
er
gy
en
re
o
en
tt
1
ch
ar
sis
ta
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..
eo
cu
rr
sq
ua
r
th
e
to
1
ch
ar
ge
1
ce
.
1
po
w
A. charge to the square of the
separation distance.
B. current to resistance.
C. energy to charge.
D. power to current.
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