Download Chapter 22 - Hingham Schools

Current Electricity
Electrons
e-
P
n
nucleus
Flow of Electrons (Path)
Electrons Flow
-- - - - - - - - +- e e e eee e e e e
Conventional Current
Conventional
Current
Flows
from
+
to
Current
Flow of Electrons
Metals - Free Electrons
e
e
e
e
e
Current
Flow of charge (q)!
q - Coulomb(C)
6.24 X 1018 electrons
e e e eee e e e e ee e ee e
Current
e e e eee e e e e ee e ee e
Amount of charge
passing a point in a
second.
Current
Symbol - I
Unit – Ampere (Amps)
Amperes - A
Current =
Charge
Time
Current
Current =
I=
Charge
Time
Q
t
Current
Coulomb
Ampere =
Second
C
1A=1
S
Force
e e e eee e e e e ee e ee e
Voltage
Potential Difference
Electromotive Force (EMF)
Source of Electrons(Force)
Voltage
Symbol - V
Unit – Volt
Volt - V
Resistance
Opposition to Current Flow
High Resistance
Insulator
Resistance
Opposition to Current Flow
Low Resistance
Conductor
Resistance
Opposition to Current Flow
High and Low Resistance
SemiConductor
Resistance
Symbol - R
Unit – Ohm
Ohm - Ω
Putting it all Together
Load
Source
Path
Schematic Diagram
I
Path
_
V
Source+
R
Load
Mathematical Equation
I
_
V
+
V = IR
R
Ohm’s Law
Ohm’s Law
The mathematical
relationship between
Current, Voltage and
Resistance.
Ohm’s Law Wheel
Find: V
V
V
=
IR
IR
Ohm’s Law Wheel
Find: I
V
V
I R I=
R
Ohm’s Law Wheel
Find: V
V
V
I R R=
I
Example
I
_
V=10v
+
R=500Ω
Example
V
I R
Given: V=10v
Find: I = ?
R=500Ω
V
10V
Equation: I =
=
R
500Ω
I = 0.02A = 20mA
Homework:22-1
Prob: 1,3,4,8,9,
11,14,17,20
Page 526, 527
Due: 3/20/07
Power
Power measures the
rate at which energy is
transferred. In the case
of electric current,
charge is being
transferred
Power
Symbol - P
Unit – Watt
Watt - W
Power
Power = Current X Voltage
P = IV
Power Wheel
Find: P
P
P
=
IV
IV
Power Wheel
Find: I
P
P
I V I=
V
Power Wheel
Find: V
P
P
I V V=
I
Power Equations
P
P
=
IV
IV
2
P=I R
2
V
V
P
=
IR
R
Schematic Symbols
Conductor
Switch
Fuse
Capacitor
Resistor
Variable Resistor
Schematic Symbols
Battery
V
A
dc generator
Voltmeter
Ammeter
Connection No Connection Ground
Schematic Diagrams
Schematic Diagrams
_
R1
V
R2
+
A
V
Meter Placement
Voltmeters are placed parallel
to the component being
measured.
Ammeters are placed in series
with the component being
measured.
Using Electric Energy
Energy used in an
Electric Circuit.
P = E/t
E = Pt
Using Electric Energy
E = IVt
2
E = I Rt
2
E = (V /R)t
Example
_
V=100v
R=500Ω
+
How much energy is
used in 1minute???
Example
Given: V=100v
R=500Ω
t=1min=60s
Equation:
E=
Find: E = ?
2
Vt
R
2
(100V) (60s)
= 1200J
E=
500Ω
Homework:22-2
Practice
Problems: 11-17
Page 517, 522
Due: 5/29/03
Transmission of
Electric Energy
Minimize Power Losses
P=
2
IR
Decrease Current
Increase Voltage - 500,000V
The Kilowatt-Hour
The Electric Company charges
you for the amount of energy in
Kilowatt-Hours.
A Kilowatt-Hour is equal to
1000W delivered continuously for
1 hour(3600s).
The Kilowatt-Hour
1kWh = (1000W)(1 hour)
1kWh = (1000J/s)(3600s)
1kWh = 3.6
6
X10
E = Pt
J
Kilowatt-Hour Example
A TV set draws 2.0A at 120V
when operating. If the set is on 5
hours a day for 30 days, how
much does it cost to run the set?
1 kilowatt-hour cost $0.12.
Kilowatt-Hour Example
Given: V=120v
I=2A
t=(5h/day)(30days)
t=150h
Find: E = ?
Cost
Kilowatt-Hour Example
Equation: E = Pt
E = Ivt
E = (2A)(120V)(150h)
E = 35000Wh = 35kWh
Cost = (35kWh)($0.12)
Cost = $4.20
Homework:22-3
Practice
Problems: 18-20
Section Review
Page: 525
Due: 5/30/03