Download Psc CH-21 Electric Fields

An electric force of
-5
4.5 x 10 N is measured
between two particles. One
particle has a charge of
-6
2.0 x 10 C & the other has a
-8
charge of 3.0 x 10 C.
Calculate the distance
between them.
Chapter 21
Electric
Fields
Electric force like
gravitational force is
inversely proportioned
to the square of the
distance between the
two points of concern
Electric Field (E)
•A vector quantity that
relates the force exerted
on a charge to the
amount of the charge
Electric Field (E)
Fon q
E =
q
Electric Field (E)
Fon q = qE
Calculate the electric
field strength when a
25 N force is exerted
on a charge of + 5.0 x
-6
10 C
Typical Field Strengths
Field
TV tube
Spark r
H orbital
Value (N/C)
5
1 x 10
6
3 x 10
11
5 x 10
Electric Field Lines
•Lines representing
the force vectors in
an electric field
Electric Field Lines
+
Electric Field Lines
-
Electric Field Lines
+
-
Electric Field Lines
•Always point
from positive to
negative
Electric Field Lines
•Do not exist , but
provide a model
of a field
The electric field
between two
parallel plates is
uniform
+
-
Electric Potential
•The electric
potential difference
of charges
measured in volts
Electric Potential
•As with heat, we
can only measure
potential difference
(DV)
Electric Potential
Difference (DV)
•The change in
potential energy
per unit charge
Electric Potential
Difference (DV)
•The work done
moving a charge
thru a field charge
Electric Potential
Difference (DV)
•Measured in J/C
•J/C = volt (V)
Electric Potential
Difference (DV)
W on q
DV =
q
Electric Potential
Difference (DV)
DU = W
Electric Potential
Difference (DV)
DUq
DV =
q
Electric Potential
Difference (DV)
W on q
DV =
q
Electric Potential
Difference (DV)
W = Fd
Electric Potential
Difference (DV)
Fd on q
DV =
q
Electric Potential
Difference (DV)
F
DV = x d
q
Electric Potential
Difference (DV)
F
E =
q
Electric Potential
Difference (DV)
DV = Ed
Basic Equations
•V = Ed
•W = qV
•F = qE
Equipotential
•When the electric
potential
difference is 0
Equipotential
•Charge rearranges
itself to reach
equipotential
Equipotential
•When two spheres have
the same charge, the
larger one has lower
electric potential
Equipotential
•When two spheres have
the same electric
potential, the larger one
has the greater charge
Equipotential
•When a charged object
comes in contact with a
neutral one, the charge is
equally distributed
Equipotential
•Because of the size of
Earth, when objects
touch Earth, their charge
is passed to the Earth
Grounding
•When a charged object
touches Earth, all its
charge flows to Earth
creating equipotential
Electric Fields
•All charges are on the
outside of a conductor
Electric Fields
•In pointed object, the
field strength is
greatest at the point
Capacitor
•A device designed to
store a charge
Capacitance
•The ratio of charge
to electric potential
difference
Capacitance (C)
q
C = DV
Farad (F)
•Unit for capacitance
measured in coulombs
per volt: F = C/V
Basic Equations
•V = Ed
•W = qV
•F = qE
•q = CV
-6
10
A charge of 1.6 x
C
is stored to create a
capacitance of
-3
4.0 x 10 F acting over
2.0 mm. Calculate:
V, E, F, & W
-6
10
A charge of 1.5 x
C
is stored to create a
capacitance of
-3
4.0 x 10 F acting over
2.0 mm. Calculate:
V, E, F, & W
-4
10
A charge of 3.2 x
C
is stored to create a
capacitance of
8.0 mF acting over 4.0
mm. Calculate:
V, E, F, & W
-6
10
Charge =1.6 x
C
-3
Force = 3.2 x 10 N
Distance = 64 nm.
Calculate:
V, E, C, & W
Calculate:
-144
3.2 x 10
162
x 1.5 x 10
-256
 8.0 x 10
175
 7.5 x 10
122
x 4.0 x 10 =
144
10
Calculate: 3.2 x
162
x 1.5 x 10
-254
 8.0 x 10
-175
 7.5 x 10
125
x 2.0 x 10 =