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ELECTRICITY
Part 1: Electrostatics.
►One
of the three basic energy use
sectors.
Electricity Generation by Source
67% Fossil Fuel
Electricity Generation by Source
77.5% Fossil Fuel
Electric Power Generation
1950-2005
Electrostatics
► Study
of charges that are NOT moving.
► What is Charge?
► A new property of matter. Similar to mass.
► Mass creates and responds to gravitational
fields
► Charges create and respond to electric
fields.
► There
are two types of charges (Ben Franklin):
 positive (+)
 negative (-)
► Symbols
for charge are q or Q
► Units of charge: Coulomb (C)
► A Coulomb is a lot of charge. Usually deal in
micro coulombs and less in electrostatics.
► Fundamental charge: Magnitude of the charge
on an electron or proton.
►e=1.602 x 10-19 C
► Like charges repel, Unlike charges attract.
Definitions
► Conductor:
Material that charges are free to
move around in. Examples: metal (silver is best
but copper is almost as good)
► Insulator (Dielectric): Material that charges are
NOT free to move around in. Examples: glass,
quartz, wood.
► Semiconductor: Can behave as either depending
on conditions: Silicon, Germanium, GalliumArsenide.
Forces on Electric Charges
► Coulomb’s
Law – for point charges and
spherical charges
kq1q 2
F 2
r
N·m
k  9 x 10
2
C
9
2
Electric Force
► In
a hydrogen atom the proton and electron are
separated by 5.3 x 10-11 m
► What
is the electric force between the proton
and the electron?
Electric force strength
10
11
13
5.
x
36
4.
x
10
-1
8
N
8.
2
x1
08
9
0%
N
0%
N
0%
N
0%
01
D.
x1
C.
60
2
B.
1.602 x 10-19 N
8.2 x 10-8 N
4.36 x 10-18 N
5.13 x 1011 N
1.
A.
Forces on Electric Charges
► Gravitational
force on a mass:
► F = mg
► Electric force on a charge:
► F = qE
► E (electric field) = F/q is the force per
unit charge that a given charge
experiences. (vector)
► In general E is not constant in space and
time.
► If
we move a charge in an electric field, we
do work on it.
► W = Fd = (qE)d
► Define Voltage as V = Ed (uniform field)
► Note V = W/q (J/C): work done per unit
charge in moving it through an electric field.
► V is potential energy per unit charge
► Equivalent to raising mass up in a
gravitational field.
Work done by electricity
► What
is the work done in moving a charge q =
1.602 x 10-19 C through 120 V?
►
Work done in moving charge
J
10
-1
7
9
01
1.
92
x
x1
0%
J
0%
24
0
0%
J
0%
60
2
D.
1.
C.
J
B.
120 J
1.602 x 10-19 J
1.92 x 10-17 J
240 J
12
0
A.
UNITS OF E & V
►V
►E
= PE/q (Joule/Coulomb = Volt)
= F/q (Newton/Coulomb)
OR
► E = V/d (Volt/meter)
CAPACITOR
► Device
for storing
charge
► Two conductors
separated by an
insulator.
► Battery moves charge
from one plate to
another.