Download Static electric charge

Unit C: Characteristics of Electricity
(Physical Science: Physics)
Wednesday, July 5,
2017
1
Chapter 6 - Static electric charges collect on
surfaces until given a path to escape
Outcomes
• Demonstrate and analyze characteristics of
static electric charges and current electricity,
including historical and cultural understandings
Wednesday, July 5,
2017
2
Static Electric Charge
• Static electric charge– A charge on a
substance that stays in
the same place
Examples of Static Charge
• Lightning-
http://www.youtube.com/watch?v=gKPwkau0Dh0&
feature=related
http://www.youtube.com/watch?v=HLcFHo2HR7I&
feature=related
• Static cling-
Examples of Static Charge
• Static shock-
6.1 The Characteristics of Static Electric Charges
• Solid materials are charged by the transfer of
electrons
o Rubbing a balloon with your hair does not
create electrical charges. All matter has
electrical charges they are just normally
neutral (equal protons/positive and
electrons/negative). The rubbing transfers the
electric charges from one object to another
this phenomenon is called static electricity the
study of static electricity is called
electrostatics.
Wednesday, July 5,
2017
6
Electric Charge
• There are two types of electrical charges:
positive and negative
• If something is positive it has lost electrons. If
something is negative it has gained electrons.
Charging an item by “rubbing” transfers
electrons making something electronically
charged.
Wednesday, July 5,
2017
7
+
-
Laws of Electric Charge
• Unlike charges attract one another
• Like charges repel one another
• Charged objects attract neutral objects
The Law of Electric Charges
A Model for the Electrical Nature of Matter
• Model of the Atom
Wednesday, July 5,
2017
10
There are three ways for something to be
electronically charged
1. Friction
2. Contact
3. Induction
Wednesday, July 5,
2017
11
Producing Static Electricity
• Charge by Friction
• Electric charge is transferred by rubbing object
together
• Friction can remove electrons from an object
Producing Static Electricity
We know which
object will cause
which charge when
caused by friction
using the
Electrostatic Series
Table 6.2 p. 208
(Items above become negatives)
• Rubber
• Ebonite
• Polyethylene
• cotton
• silk
• wool
• glass
• acetate
• fur/hair
(Items below become positives)
Insulators
An electrical insulator is a substance in which
electrons cannot move freely from atom to atom.
Conductors
A conductor is a substance in which electrons can
move freely from one atom to another.
Wednesday, July 5,
2017
14
Static Electricity and Winter
• Static electricity is much worse in the winter
because the air is so dry and dry air is a very
good insulator. Water droplets transfer electrons
very easily and do not allow large charges to
build up.
Read Pages 202 - 211
Learning Checkpoint p. 209 # 1 - 5
6.1 Check and Reflect # 1 – 7 (p. 211)
Wednesday, July 5,
2017
15
6.2 The Transfer of Static Electric Charges
• In charging by contact, a neutral object gains the
same type of charge as the charged object
touching it.
• In charging by induction, a neutral object gains
the opposite charge as the charged object
DIAGRAM
Wednesday, July 5,
2017
16
Charging By Contact
• A charged item can transfer its charge by
touching a charged or even an uncharged item.
http://www.sciencewithmrnoon.com/electroscope.s
wf
Wednesday, July 5,
2017
17
Removing Static Electricity
• Discharge (neutralize)– When excess electric charge is removed from
an object.
• Discharge can be quick and explosive (lightning)
• Discharge can be unnoticed (fabric softener sheet)
http://www.youtube.com/watch?v=R7cgazVkhTk&fe
ature=related
Removing Static Electricity
• Grounding
– Connecting the object to the earth
• The charge is shared with the entire earth
• Discharge at a point
– Objects made into a point have electrons
pushed off the end.
Induction
• Induction - something is made to happen without
contact
Induced Charge Separation
• A slight shift in position of electrons that
produces opposite charges on the two sides of a
particle
Wednesday, July 5,
2017
20
Producing Static Electricity
Charge by Induction
– Neutral object becomes charged when a
charged object is brought near it.
• Induced charge can become more permanent if a
ground wire is attached to it.
http://www.sciencewithmrnoon.com/electroscop
e.swf
Charging Conductors by Induction
• It is possible to induce a charge on a conductor
and even give it a permanent charge.
Wednesday, July 5,
2017
22
Read Pages 213 - 219
6.2 Check and Reflect # 1 – 9 (p. 219)
Wednesday, July 5,
2017
23
Detecting Static Charge
• Electroscope -a device used to detect the
presence of charge.
– usually constructed with a metal plate or
sphere at the top of a metal post with thin foil
leaves hanging from the bottom of the post
http://www.regentsprep.org/Regents/physics/ph
ys03/aeleclab/nerscope.htm
6.3 Electrostatics in Our Lives
• Some First Nations and Métis peoples have an
intimate spiritual understanding of lightning in
terms of Thunderbird
• Lightning rods are used to prevent damage to
buildings
Wednesday, July 5,
2017
26
Dangers of Static Electricity
• Cause fires
https://www.youtube.com/watch?v=tuZxFL9cGkI
• Can wreck electronics (need grounding wire)
• Can hurt (shock) or cause death (10-9)
http://www.youtube.com/watch?v=CpxKEGdfDxI&f
eature=related
Uses of Static Electricity
• Electrostatic air cleaners
– Removes dust and other particles by the
attraction of unlike charges
• Electrostatic spray painting
– The paint and the object to be painted are
given opposite charges
http://video.google.com/videoplay?docid=860069260229630847
Uses of Static Electricity
• Fabric softener sheets
– Allows electric charge to move in between
clothes instead of building up.
• Photocopiers
• Cell phones and car radios
• Electrostatic precipitators work by creating
charged waste particles and using electrostatic
attraction to remove particles
Wednesday, July 5,
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30
Discharge at a Point
• For items that are not attached to the earth like
an air plane grounding will not work. Airplanes
use a method of discharging at a point of a rod
which effectively discharges a charge very
quickly.
Wednesday, July 5,
2017
31
Read Pages 223 - 228
6.3 Check and Reflect # 1 – 11 (p. 228)
Chapter 6 Review p. 232 – 233 # 1 - 25
Wednesday, July 5,
2017
32
Chapter 7 – Current electrical energy is the
flow of electrons in a closed circuit
Outcomes
• Demonstrate and analyze characteristics of
static electric charge and current electricity,
including historical and cultural understanding
• Analyze the relationships that exist among
voltage, current, and resistance in series and
parallel circuits
Wednesday, July 5,
2017
33
7.1 Voltage, Current, and Resistance
• Static Electricity is the build up of electrons and
the transfer of an electrical charge. The flow or
movement of electric charges from one place to
another is called electric current.
Wednesday, July 5,
2017
34
Current Electricity
• The movement of electric charge from one
place to another.
• Electric current is the rate of movement of
electric charge through a conductor.
• The electric current passing through your house
is different than static electricity it is flowing
through a controlled path called an electric
circuit.
• Electric circuits are used to convert electrical
energy into other forms of energy we need.
Wednesday, July 5,
2017
36
Voltage
• Potential (Voltage)– IS THE ELECTRIC POTENTIAL PER CHARGE
MOVING BETWEEN TERMINALS.
– THIS IS LIKE THE ELECTRIC PRESSURE
PUSHING THE ELECTRONS.
– VOLTAGE DOES NOT MOVE, IT PUSHES THE
ELECTRONS.
http://faraday.physics.utoronto.ca/IYearLab/Intros/
DCI/Flash/WaterAnalogy.html
Electric Potential (Voltage)
• Voltage is the difference in electric charge
between two points
• The energy each electron has is called the
electric potential of the electron. The unit used
to measure electric potential is the volt.
Pump Analogy
• Voltage can be compared to the pressure of
water in a hose. The higher the pressure, the
faster the water will flow through the hose.
Similarly, the higher the voltage of the electricity,
the faster it will flow from a source of electricity
to an end use.
Wednesday, July 5,
2017
38
High Voltage
Low Voltage
High Voltage
Low Voltage
Voltage
• Potential (Voltage)
cont’d– Measured in volts (V)
– Measured using a
voltmeter.
Electric Current
• Electric current is a measure of the rate at which
electric charges move past a given point in a
circuit. The unit used to measure electric current
is ampere.
Wednesday, July 5,
2017
42
Current
• Current– The measure of the rate at which electric
charges move past a given point in a circuit.
– Measures the amount of electricity passing a
point.
– Measured in amperes (A)
– Measured using an:
• Ammeter- larger currents
• Galvanometer- smaller currents
• Amps can be compared to the volume of water
that flows through a hose. The volume of water
that flows past a certain point in a specific
amount of time can be measured. The rate of
the electric current is dependent upon the
voltage and resistance. A circuit with high
voltage and low resistance will have more amps
(greater number of electrons passing through
the circuit) than a circuit with low voltage and
higher resistance.
Wednesday, July 5,
2017
44
High Current
Low Current
High Current
Low Current
Resistance
• Resistance
– The measure of an objects opposition to the
passage of a steady electrical current
• Measured in ohm’s (Ω)
• Measured using an ohmmeter
Electrical Resistance and Ohm’s Law
• The ability to impede the flow of electrons is
called electrical resistance. A resistor is used
for this purpose. Electrical resistance R is
measured in ohms.
Wednesday, July 5,
2017
48
Low
Resistance
High
Resistance
Low
Resistance
Electrochemical Cell
• An electrochemical cell generates electricity by
creating an imbalance of charges between
terminals
Primary Cells
• Primary cells use materials in a chemical
reaction to create electricity.
Wednesday, July 5,
2017
50
• Primary cells- Disposable cells
• Secondary cell- reusable cells
All cells contain:
Electrodes- Metal plates that are placed in the electrolyte
Electrolytes- Chemicals that conduct electric current
Positive terminal- Place where positive charges collect
Negative terminal- Place where negative charges collect
• A primary wet cell or voltaic cell use two metals
(usually copper and zinc) as electrodes and use
a liquid (sulphuric acid) as an electrolyte.
Copper gives its electrons to zinc and when
connected the electrons are allowed to flow.
Wednesday, July 5,
2017
52
Electrical Sources
• Cells can be:
– Wet cells- electrolyte is a liquid
• Easy to make with available chemicals
• Hard to transport and quite large
Electrodes
Electrolyte
Electrical Sources
– Dry cells- Electrolyte is a paste
• Easy to transport and very compact; sealed
• Special and sometimes more dangerous chemicals are
required.
Secondary Cells
• A secondary cell can be discharged and
recharged because it does not use chemicals.
• Models can be mental, mathematical, or a
combination. Scientific models can help you
communicate your ideas.
Read Pages 234 - 244
Learning Checkpoint p. 242 # 1 - 5
7.1 Check and Reflect # 1 – 14 (p. 244)
Wednesday, July 5,
2017
55
7.2 Series Circuits and Parallel Circuits
Wednesday, July 5,
2017
56
Electrical circuits
•
Electrical circuit–
•
Controlled path of flowing electricity in a complete circle
Contain 4 parts
1.
2.
3.
4.
Source- Where electricity comes from.
Load- Where the electrical energy is transferred.
Control- What starts and stops the electricity.
Connectors- The path where the electricity runs.
Load
Source
Control
Connector
Electrical circuit- Source
• Cells- Converts chemical energy into
electrical energy.
• Batteries- combination of 2 or more cells
• Generators-a device that converts
movement into electrical energy
• Photoelectric cells- a cell that converts
light directly into electrical energy
Cell
Generator
Battery
Photoelectric Cell
Electrical Load
• An electrical load is anything that converts
electrical energy into any form of energy we
need.
• Resistor – circuit component designed to
provide a specific amount of resistance to
current flow.
• Lamp/bulb – An electrically energized source of
light
• Motor – A device or machine that converts other
forms of energy into mechanical energy. Electric
to mechanical
Wednesday, July 5,
2017
61
Electric circuit- Load
• Anything that converts electrical energy into the
form of energy required
–
–
–
–
–
–
–
Light bulb (light energy)
Toaster (heat energy)
Television (light and sound energy)
Computer (light and sound energy)
Fan (mechanical energy)
Music player (sound energy)
Motor (mechanical energy)
• Fuse – A safety device with a metal wire or strip
that melts when the current gets too strong,
cutting off the flow of the electrical current.
• Circuit Breaker – an additional safety device with
a metal that does not melt but instead bends
which triggers a mechanism that that turns of the
flow of electrical energy
• In a short circuit, the current does not take the
intended path back to its source
Wednesday, July 5,
2017
63
Electric Circuit Control Device
• Switch – used to open or close a circuit
• Timer and Thermostat
• Ammeter – measures current flow
– An ammeter is hooked up in series to
measure current.
• Voltmeter – measures current pressure
– A voltmeter is hooked up in parallel to
measure voltage
Wednesday, July 5,
2017
64
Electrical circuits-Connectors
• A conducting wire that provides a controlled path
for electric current to flow to each part of the
circuit
– Conductor- A substance where electrons can move
freely from one atom to another. (electric current)
– Insulator- A substance where electrons cannot move
freely from one atom to another. (Static electricity)
– Superconductor- Ceramics that conduct electricity
with no resistance at low temperatures. (bullet trains)
Conductor
e
Insulator
e
e
e
Superconductor
e
e
e
Electrical circuits
• Open circuit- circuit is not connected, switch is
open, no electricity is flowing
• Closed circuit- circuit is connected, switch is
closed, electricity is flowing
• Short Circuit- Circuit where there is not a load
attached to the circuit, no resistance. Can be
very dangerous, connectors can become
overheated and burn, cells will use up the
potential very rapidly.
Open Circuit
Closed
Circuit
Short Circuit
Electric Circuit Diagrams
• A circuit diagram is a model of an electric circuit
• Using the known symbols for some common
electrical components a schematic circuit
diagram can be used to illustrate a circuit.
Example: Simple Circuit
Four basic parts – load / conducting wire /
electrical source / control (switch)
Wednesday, July 5,
2017
70
Electrical circuits
•
Electrical circuits can be made in two
different ways.
1. Series circuit- One path of electric charge
Electrical circuits
2. Parallel circuit- 2 or more paths for electric
charge to follow (branches)
- Cell
- Battery (2 cells)
- Light
M
- Motor
V
- Voltmeter
A
- Ammeter
- Switch
pole)
(1
Making a Circuit Schematic Diagram
•Create a circuit that has one cell powering 1 light
that is controlled by a switch.
•Create a circuit with a 3 cell battery that has 2 lights
connected in series all controlled by one switch.
•Create a circuit with a 3 cell battery that has 2 lights
connected in parallel all controlled by one switch, with
another switch controlling just one of the lights.
Cells in Series and Parallel
• Cells in series are connected end-to-end and
have an additive voltage.
Pump Analogy
• Series Circuit – all components are connected
end-to-end, forming a single path for electrons to
flow.
• In a series circuit, the current is constant and the
voltages across resistors adds up to the total
voltage supplied by the energy source
Wednesday, July 5,
2017
77
Electrical circuits
• Connecting cells in:
– Series- the potentials of the cells are added
together
• ie. Three 1.5V cells connected end to end has a
potential of 4.5V
+
+
+
-
-
-
= 4.5 V
• Adding resistance increases the total resistance
and lowers current
• Current is the same throughout the circuit
• The total resistance is the sum of the
resistances in the circuit
Example
Three 1.5V cells an ammeter and three resistors
(R1= 4 Ω, R2= 5 Ω, and R3=6 Ω) in series
What is the total resistance?
What is the total voltage?
Wednesday, July 5,
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• Cells in parallel are not connected end-to-end
and thus do not have an additive voltage instead
they are connected beside each other and have
twice as many electron doing one cells work.
Pump Analogy
• Parallel Circuit – all components are connected
across each other, forming exactly two sets of
electrically common points.
• In a parallel circuit, the voltages across loads are
constant and the currents on each path add up
to the total current leaving the energy source
Wednesday, July 5,
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Electrical Circuits
– Parallel- the cells will last longer
• Potential remains the same
+
+
+
-
-
= 1.5V
• Adding resistance decreases the total resistance
and increases current
• The more branches there are the smaller the
resistance in each branch, the more the total
circuit current will be (additive)
• Voltage remains constant and is equal to the
source
Wednesday, July 5,
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85
Example
Three 9 V cells in parallel attached to a switch and
an ammeter in series attached to three resistors
and a voltmeter in parallel (R1= 4 Ω, R2= 5 Ω, and
R3=6 Ω)
What is the total voltage?
Wednesday, July 5,
2017
86
Circuit
Voltage (volts)
Current (amps)
Resistance
(ohms)
Series
Circuit
Each load uses a
portion of the total
energy supplied by
the battery
The current is
the same
throughout the
circuit
The current decreases
when more resistors
are added if the energy
remains the same
Parallel
Circuit
Each load uses all
the energy supplied
by the battery
The current
divides into
different paths.
A pathway with
less resistance
will have a
greater current
Adding resistors in
parallel decreases the
total resistance of the
circuit if the energy
remains the same
Wednesday, July 5,
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88
Electrical circuits
• Pro’s and cons of series and parallel
circuits.
– Series
• Pro’s
– Simple to make and easy to follow.
• Con’s
– Limited control over the circuit and when one load is
broken, the entire circuit won’t work.
Electrical circuits
• Pro’s and cons of series and parallel
circuits.
– Parallel
• Pro’s
– Lots of control over the circuit and not all loads have to
be working at the same time
• Con’s
– Much more complex and difficult to follow.
Read Pages 248 - 252
7.2 Check and Reflect # 1 – 9 (p. 253)
Wednesday, July 5,
2017
91
7.3 Ohm’s Law
• Ohms (Ω) measure resistance and can be
compared to the diameter measurement of a
hose. A smaller diameter hose will allow less
water to flow through than a larger diameter
hose. Similarly, a thinner wire increases
resistance, causing a lesser amount of electricity
to be transmitted because it is encountering
resistance in the wire. To reduce resistance,
certain metals are used to conduct electricity,
such as copper, which allows electrons to flow
easily.
Wednesday, July 5,
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92
• When electrons flow through a conductor
electrical resistance causes a loss of electrical
potential (volts). This loss is referred to as
potential difference.
Wednesday, July 5,
2017
93
Ohm’s Law
• “the potential difference between two points on a
conductor is proportional (directly related) to the
electric current flowing through the conductor”
• We refer to potential difference as voltage drop
b/c voltage is lost or “dropped” across a
conductor.
Wednesday, July 5,
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94
• We can calculate voltage drop by:
• Potential difference (voltage drop) = electric
current x Electrical Resistance
• V=IxR
• Potential difference (V) is measured in volts (V)
• Electric current (I) is measured in amperes (A)
• Electrical Resistance (R) is measured in ohms
(Ω)
• Ohm’s Law V = I x R, describes the
relationship between voltage, current and
resistance
Wednesday, July 5,
2017
95
Solving Science Problems Involving Formulas
5 step process
I.Data – record the given and required data
II.Formula – write the required formula
III.Substitute – place the data in the formula
IV.Calculate – do the math (calculator)
V.Statement – write a sentence to paraphrase your
work
Wednesday, July 5,
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96
Example Problem 7.1
A current of 4.0 A flows through a 40 Ω resistor in
a circuit. Calculate the voltage.
Example Problem 7.2
A 30 V battery generates a current through a 15 Ω
resistor. How much current does the battery
generate?
Example Problem 7.3
An electric stove is connected to a 240 V outlet. If
the current flowing through the stove in 20 A, what
is the resistance of the heating element?
Wednesday, July 5,
2017
97
Example
Three 1.5V cells, a switch, an ammeter and three
resistors (R1= 4 Ω, R2= 5 Ω, and R3=6 Ω) in series
a.What is the total resistance?
b.What is the total voltage?
c.What is the current for this circuit?
d.What is the voltage drop for each resistor?
Wednesday, July 5,
2017
98
Example
Three 9 V cells in parallel attached to a switch and
an ammeter in series attached to three resistors
and a voltmeter in parallel (R1= 4 Ω, R2= 5 Ω, and
R3=6 Ω)
a.What is the total voltage?
b.What is the current through each resistor?
c.What is the total current?
d.What is the total circuit resistance?
Wednesday, July 5,
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Practice problems p. 260 – 261 (3)
Read Pages 258 - 264
7.3 Check and Reflect # 1 – 6 (p. 264)
Chapter 7 Review p. 266 – 267 # 1 - 15
Wednesday, July 5,
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100
Chapter 8 – We can reduce our electrical
energy consumption and use renewable
energy resources to produce electrical energy
Outcomes
• Assess operating principles, costs, and
efficiencies of devices that produce or use
electrical energy
• Critique impacts of past, current, and possible
future methods of small and large scale
electrical energy production and distribution in
Saskatchewan
Wednesday, July 5,
2017
101
Energy
• Energy- The ability to do work.
• There are many forms of energy
–
–
–
–
–
–
–
Light
Sound
Movement (mechanical)
Heat
Electricity
Nuclear
Chemical
Thermodynamics
• Thermodynamics is the study of moving
energy.
• The first law of Thermodynamics says
that: Energy cannot be created or
destroyed.
– Energy can only be transformed from one
form to another.
Electricity
Light
Energy Transformations
• Toaster- Electrical energy is converted to
heat energy.
– The heat is produced by resistance inside the
toaster (friction)
Electricity
Heat
Energy Transformations
• Light Bulb- Electrical energy is converted
to light energy
– Light is produced by the resistance inside the
light bulb.
Electricity
Light
Energy Transformations
• Speaker- Electrical energy is converted
into sound energy.
– Sound is produced by having electricity turn a
magnet on and off. (electromagnet)
Electricity
Sound
Energy Transformations
• Electric motor- Electrical energy is converted into
motion (mechanical) energy.
– Motion is produced by creating an alternating
magnetic field. (electromagnet)
Electricity
Motion
Electromagnets
• A coiled wire carrying electrical current
produces a magnetic field around it.
– It acts like a magnet.
N
S
Electromagnets
• If a piece of metal is inserted into the coil,
the metal will become magnetized.
• The magnetism will only last when
electricity is running through the circuit.
With a
anclosed
open circuit,
circuit, there
there is
is no
an
magnetic
electric
field.
field.
N
S
Electromagne
t
Metal
plate
Permanent
Magnet
Brus
hes
Wire coil
N
S
Running
electricity
through a wire
The similar poles
coil produces a
‘repel’ each
magnetic field
other
Whencausing
the gap
the
wire
coilcoil
to
in the
wire
rotate.
reaches the
The
wire coil
brushes,
the
will
continue
magnetic
fieldto
rotate
in the
disappears.
same
direction,
This process
which
will
continues
produce
producinga anew
Thermodynamics
• The second law of thermodynamics tells
us that every time energy is transformed
from one type of energy to the next type,
some of the energy is transformed into an
unusable form.
– Not all the energy is converted.
Electricity
Sound
Heat
Light
Energy Loss
• Toaster- Electrical energy is converted to
heat energy.
– Energy is lost in the production of light and
sound.
Light
Electricity
Heat
Sound
Energy Loss
• Light Bulb- Electrical energy is converted
to light energy
– Energy is lost as heat
Heat
Electricity
Light
Energy Loss
• Speaker- Electrical energy is converted
into sound energy.
– Energy is lost as heat and motion.
Heat
Electricity
Sound
Motion
Energy Loss
• Electric motor- Electrical energy is
converted into motion (mechanical)
energy.
– Energy is lost as heat and sound.
Heat
Electricity
Motion
Sound
Generating electricity
• We have discussed several sources of
electrical energy;
– Cells
– Batteries
– Photoelectric cell
– Generator
Generating electricity
• The majority of our daily electricity comes from
electricity generating stations.
• All generating stations work on the same
principals.
• We discussed earlier how current electricity in a
coil produces a magnetic field. The reverse
process is used to produce current electricity.
• A moving magnetic field produces current
electricity.
In the presence
of a magnet, the
electrons are
drawn in by the
magnetic field.
N
S
e
e
e e ee e ee e
e
e
e
e
e
When the magnet moves, the
electrons will be pulled along with
it. The electrons are now moving,
this is current electricity.
e
Generating electricity
• A generator uses the same materials as
an electric motor, but everything happens
in reverse.
– Electric motor- current electricity produces the
spinning coil.
– Generator- a spinning coil produces current
electricity
N
e
S
e
e
e
e
The electrons are
drawn to one side
of the magnet so
the the
electrons
flow in
As
coil rotates,
one
direction are
to that
the electrons
side ofdrawn
the magnet.
again
to the
one side of the
As the coil
magnet so the
continues to rotate,
electrons make the
current electricity
trip again
continues to flow.
e
Generating Electricity
• There are two types of electricity that can
be created:
– Direct current (DC)- Electricity flows in one
direction (cells, generator shown)
– Alternating current (AC)- Electricity switches
directions as the coil rotates.
Direct Current (DC)
e
Alternating Current (AC)
e
e
e
e
e
e
e
e
Generating Electricity
• There are many different ways to turn the
wire coil inside the generator.
• The coil is attached to a turbine, and the
turbine is rotated by:
– Steam (coal, nuclear, natural gas, biomass)
– Water
– Wind
Transporting Electricity
• Electricity has to be moved from the
generating stations to peoples houses.
Fromhigh
The
these
voltage
substations,
InThe
your
electricity
power
neighborhood,
electricity
lines
is go in
into
another
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8.1 Renewable and Non-Renewable Energy
Resources for Generating Electrical Energy
• Renewable Energy Resources – resources that
constantly replenish themselves
E.g. Solar, wind, biomass, hydroelectric,
geothermal, tidal
• Non-renewable Energy Resources – resources
that cannot be replaced in a reasonable amount
of time
E.g. Fossil fuels (oil/coal) and nuclear
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131
• Sustainability – with respect to electrical energy
refers to a consideration of social, economic,
and environmental aspects of its production and
use now and in the future
• We need to move toward sustainability in our
resources
• Electrical energy generators transform the
energy of motion into electric current
Read Pages 268 - 279
Learning Checkpoint p. 276 # 1 – 3
Learning Checkpoint p. 277 # 1 – 3
8.1 Check and Reflect # 1 – 9 (p. 280)
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132
8.2 Reducing Our Electrical Energy Consumption
Making the Most of Energy Resources
• Input energy – chemical energy used to make
electricity
• Output energy – actual electric energy
produced
• Efficiency = useful energy output / energy input
• % efficiency = useful energy output / energy
input x 100%
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133
Efficiency
• Efficiency is the comparison between the
amount of useful energy produced (output
energy) and the original amount of energy
used (input energy).
% efficiency = Useful Output Energy x 100%
Input Energy
Example
• Determine the percent efficiency of a bulb that
uses 2000 J of electrical energy to produce 400
J of light energy.
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135
Can you ever have an appliance
than is 100% efficient?
No
Electrical Energy Use in the Home
• Electrical Energy = Electrical Power x time
interval
• E = P x Δt
• E = kW∙h (Electrical energy consumption is
usually measured in kilowatt-hours)
• P = kW
• Δt = h
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137
Example
• How many kilowatt hours of electrical energy are
used in one month by a clothes dryer that has a
power rating of 5 kW and is operated for 4.5 h?
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2017
138
Cost
• Cost = Electrical Energy (kW∙h) x rate (cost per
kW∙h)
Example
• Calculate the cost of the electricity needed to
operate a refrigerator/freezer (500 W) for one
month if it uses 75 kW∙h of energy. The rate
charged for electricity is $0.08 / kW∙h.
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139
• The EnerGuide label shows how much energy
an appliance will use in a month of average use
• Energy Star appliances are the most efficient
appliances in their class
Read Pages 284 - 290
Learning Checkpoint p. 286 # 1
Practice Problems # 1 – 3 p. 287
8.2 Check and Reflect # 1 – 13 (p. 290)
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140
Measuring Electrical Energy
•
•
•
•
Energy – the ability to do work
Electrical energy (E) – energy transferred to
any electrical load by moving electric charges
Electrical energy is measured in joules. A
joule is a small amount ~ light a 100 W bulb for
1 / 100th of a second
Also measured in Watt hour which is 3600
times as much as a joule or kilowatt (1000 W)
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141
Calculating Electrical Energy
• E = V x I x Δt
• where
• E – electrical energy measured in Joules (J) for
seconds or Watt hours (W∙h) for hours
• V – voltage drop measured in volts (V)
• I – electric current measured in amps (A)
• Δt – time interval measured in seconds or hours
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Example
• Calculate the energy released from a battery in
a flash light that was on for 4.5h with a voltage of
6V and a current of 0.35 amps.
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143
The Rate at Which Energy is Used
• Electrical Power (P) – measure at which
electrical energy is used measured in watts
• Electrical power = electrical energy / time
interval
• P = E / Δt
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144
Example
• Calculate the power of a toaster that uses 72000
J of energy for 50s
Or
P = E / Δt = V x I x Δt / Δt = V x I
Example
• Calculate the power of a vacuum cleaner if the
operating voltage is 120 V, and the current
flowing through it is 7.90 amps
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2017
145
Hand-Out – Electricity Calculations
Chapter 8 Review P. 294 – 295 # 1 – 21
Unit C Review P. 299 – 301 # 1 - 35
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146