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OUTCOME QUESTION(S):
S1-3-08:
What is “electricity” and how is it created?
Vocabulary & Concepts
Electricity
Generator
Creating “Electricity”
• Different sources exist for creating energy from
free electrons and generating an electric current
•
•
•
•
Batteries
Solar Panels
Hydro Dams
…
What other ways have
you seen to create
electricity?
(Current) Electricity:
the flow of electrons around a circuit.
Most electricity is creating using two basic steps:
1. Remove electrons from one location (takes energy)
2. Let electrons flow back (releases energy)
Essentially just
converting one form of
energy into another
form
1. Chemical: source converts chemical energy into
electrical energy.
• Reaction separates electrons from metal (+)
• Energized electrons collect at other metal (-)
• Electrons flow back to (+) metal
More detail to come on
batteries….
2. Thermoelectric: source converts heat energy
into electrical energy.
• Metals heated at one end and cooled at other
• Energized electrons flow towards cool side
Called a thermocouple / thermopile
Thermocouples are used as safety control
devices in furnaces, engines and appliances
3. Photoelectric: source converts solar energy into
electrical energy.
• Light energy separates electrons from material
• Energized electrons accumulate on “collector”
• Creates a weak flow of electrons
Remember: visible light is just one form of wave around us Some are low energy (radio wave) some high energy (x-ray)
4. Piezoelectric: source converts mechanical
energy into electrical energy.
• (some) Materials polarize when squeezed
various crystals, ceramics, bone
• Creates charge separation across the faces
• Electrons flow when faces are connected
Piezo comes from the Greek word meaning pressure
The piezoelectric effect also works in reverse:
• Applying current to a crystal causes it to change
shape (vibrate)
Ultrasound machines, sonar, microphones, watches/clocks,
push lighters, all use the piezoelectric effect
5. Electromagnetic: source converts mechanical
energy into electrical energy.
• Coil of wire spinning through a magnet
creates a flow of energized electrons
• Device is called a generator
An energy source is needed to turn generator
– wood, coal, falling water, nuclear reaction…
97.6% of Manitoba energy comes from dammed water
turning the generator to create the electricity
STATIC Vs. CURRENT ELECTRICITY
SIMILAR
DIFFERENT
Both: need input of energy to
create charge
(friction or other source)
Static: displaced electrons are
localized
Both: 1st step is charge separation
2nd step is charge transfer
(neutral object or battery)
Static: brief transfer of small
amounts of charge
Current: displaced electrons
move
Current: continued transfer of
large amounts of charge
Both: will discharge (run out)
when all electric charge is
transferred back
Static: discharges randomly
Current: discharges through a
conducting path
CAN YOU ANSWER THESE QUESTIONS?
S1-3-011:
What is “electricity” and how is it created?
Vocabulary & Concepts
Electricity
Generator
OUTCOME QUESTION(S):
S1-3-09/10/12:
What do current, voltage and resistance mean for
electrons?
Vocabulary & Concepts
Cell
Coulomb
Volt
Voltmeter
Ampere
Ammeter
Resistor
Ohm
Voltage
Current
Resistance
Load
Cell: device that uses a chemical reaction to create
a flow of electrons between different materials.
NEED:
• metal to lose electrons – (-) electrode (anode)
• metal to gain electrons – (+) electrode (cathode)
• chemically reacting substance – electrolyte
The acidic lemon
juice acts as the
electrolyte to aid the
chemical reaction
The original Voltaic “wet” cell does not
have practical use today and has been
replaced by the “dry” cell - battery
Rod: (+) electrode
(cathode)
Casing: (-) electrode
(anode)
electrolyte
paste
Cell Measurements:
Electrons are measured and counted in bundles
called a coulomb:
• 1 coulomb = 6.25 quintillion (6.25 x 1018) electrons
Think of a coulomb as very, very large “dozen”
1. Voltage (V)
Electrical potential of electrons in a source:
• electrons convert their potential energy into work
Potential: unrealized ability to accomplish something
Voltage: energy the electrons have to potentially do something
• Measured by a Voltmeter
• Units: Volt (V)
E
V=
Q
• E is energy/work potential in joules
• Q is the number of coulombs
Voltage (volts) measures the potential energy
available in every coulomb of electrons
As electrons move to the other
end of the source they lose all
potential (stored) energy
1.5 Volt battery
1.5 joules of energy
released by every
coulomb of electrons
(+) electrode
(-)
electrode
550 V – typical Power station
120 V – typical wall outlet
1.5 V – typical battery
0 Volts
electrolyte
paste
1.5 Volts
2. Current (I)
The rate (speed) at which electrons move through
the conductor.
• Measured by an Ammeter
• Units: Ampere /Amps (A)
I=
Q
t
• Q is the number of coulombs
• t is time in seconds
Current (amps) measures the number of
electrons passing a point every second
1 Amp = electrons
moving at a rate of
1 coulomb per second
0.83 A – current needed for a typical light bulb
0.2 A – severe burns, heart stops, lungs stop
(“let go” threshold)
0.02 A
– breathing affected, muscles contract
0.002 A
– muscles tingle (good shock)
Its not the voltage that kills, it’s the current: the
number of electrons running through you
3. Resistance (R)
Anything that slows down electrons and takes
potential energy away in the process.
Resistors are electrical components used to control
the current and voltage to protect the device.
• Units: ohm (Ω)
The loss taken
of potential
energy as
Energy
is converted
electrons slow through a resistor is
ascalled
work
lost asdrop”
heat
theor
“voltage
eLoad
• a resistor that
converts energy for use
+
-
e●
●
Resistor
• slows electrons and
take energy as heat
Even the conducting wire provides some resistance – takes
some energy away converting it to heat
CAN YOU ANSWER THESE QUESTIONS?
S1-3-09/10/12:
What do current, voltage and resistance mean for
electrons?
Vocabulary & Concepts
Cell
Coulomb
Volt
Voltmeter
Ampere
Ammeter
Resistor
Ohm
Voltage
Current
Resistance
Load