Transcript Science 9 – Electrical Principles

A Unit 4 Review
SCIENCE 9 – ELECTRICAL PRINCIPLES
TOPIC 1 – ELECTRIC CHARGES
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When an object is charged, it has an imbalance of
electrons. Static electricity is another term used to
describe this.
You can charge different materials by rubbing
them together. Friction!
Remember, only electrons (-) move!
Ben Franklin created the Law of Charges:
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Like charges repel
Unlike charges attract
Charged objects attract uncharged objects
TOPIC 1 – ELECTRICAL CHARGES
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Conductors allow charges to move freely. (eg.
Copper wire)
Insulators hold charges stopping their flow. (eg.
plastic)
Semi conductors allow some charges to flow but
put up a bit of resistance. (eg. Silicon or Tungsten)
Superconductors offer no resistance. They can
only be made at extremely low temperatures and
are usually made of metal alloys or ceramics
TOPIC 2 - CIRCUITS
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Typically all circuits have 4 parts:
 Source like a battery or cell.
 Conductor like a copper wire
 Load something that transforms electricity
into another useful form like light (bulb!),
sound (buzzer!), or mechanical (motor!)
energy.
 Control like a switch
TOPIC 2- CURRENT AND VOLTAGE
Current is the flow of electrons.
 It is measured in amperes (A) using a
galvanometer (weak current) or an ammeter
(larger current).
 Voltage is the potential difference in energy
between two points in a circuit.
 It is measured in volts (V) using a voltmeter.
 Circuits can be compare to rivers (see p. 278)
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TOPIC 2 – CIRCUITS, CURRENT, AND VOLTAGE
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There are 2 types of circuits:
 Parallel circuits (all loads are attached to the power
source in branches)
 Series circuits (loads share the power source)
In a parallel circuit, all the loads will have the same
voltage passing through them. This means the battery
may burn out faster.
In a series circuit, the loads share the electrical
energy. What will happen if we add too many bulbs to
a series circuit?
TOPIC 3 - RESISTANCE
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All materials off resistance to the flow of electrons inside
of them. For example, a good conductor offers little
resistance so electrons can flow smoothly and quickly!
Common resistors in circuits would be Nichrome wire or
tungsten.
Resistance is measured in ohms (Ω) using an ohmmeter.
Variable resistors can change how much resistance they
offer. They can be found in dimmer switches, volume
controls, etc…
TOPIC 3 - RESISTANCE
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Ohm’s Law:
Resistance equals voltage over current:
TOPIC 3 - RESISTANCE
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Resistance increases if:
 Length
increases
 Area decreases
 Temperature increases
 The material has a high resistance
TOPIC 4 - TRANSFORMING ENERGY
Transformation
Devices
Thermal  Electrical
•Thermocouple
•Thermopile
•Thermo-electric generator
•Piezoelectric crystal
•Piezoelectric crystal
•LED (light emitting diode)
•Photovoltaic cell
Electrical  Motion
Motion  Electrical
Electrical  Light
Light  Electricity
TOPIC 5 CELLS & BATTERIES
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An electrochemical cell (aka voltaic cell) has the following
parts:
 2 metal electrodes (ex. Copper and Zinc)
 An electrolyte (contains dissolved ions/charged
particles).
 A conducting wire connecting the two electrodes.
Ions from the negative electrode (anode) to the positive
electrode (cathode) through the conducting wire.
Eventually, the negative electrode gives up all its electrons
(you can see it shrink visibly!) and the cell dies.
TOPIC 5 – CELLS & BATTERIES
Primary cells cannot be recharged.
 Secondary cells can be regcharged.
 Wet cells have a liquid electrode.
 Dry cells have a solid electrode.
 When cells are connected in series, you get a
battery
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TOPIC 6 – GENERATORS & MOTORS
An electromagnet 
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Electromagnets are created when current is passed through an
iron core.
 The more batteries or the more coils, the stronger the
magnet.
 No current = no magnet
Generators transform mechanical energy  electrical energy.
In a generator, a coil of wire rotates within a field magnet and
produces electricity.
Normally current is alternating (AC) but if we add a split ring
commutator, then you create a DC generator.
TOPIC 6 – GENERATORS AND MOTORS
The current entering our homes is AC current.
This current can be “stepped up.”
 Motors convert electrical energy  mechanical
energy.
 An electromagnet rotates within a field magnet.
When magnets repel & attract, this created a
rotating motion. This motion allows for work to
be done!
 Please see diagrams in Topic 6.
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TOPIC 7 – ELECTRICITY IN THE HOME
Power Generating Station 
 Step up transformer 
 High Voltage Power lines 
 Low Voltage Power lines 
 Step down transformer  Your Home
 Meter 
 Service Panel & Main Circuit Breaker 
 Branch Circuit Breakers 
 Branch Circuits in each room
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TOPIC 7 – ELECTRICITY IN THE HOME
Power = E/t = I x V
 Power is measured in Watts.
 Energy is measured in Joules
 Time is measured in seconds
 Current is measured in Amperes
 Voltage is measured in Volts
 Efficiency = (Eoutput/Einput) x 100%
 Try practice problems on p. 325 & 325 & 329
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TOPIC 8 – ELECTRICITY PRODUCTION AND
ENVIRONMENTAL PROTECTION
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Electrical energy can come from non-renewable
sources:
 Fossil
fuels (coal, natural gas, etc.)
 Nuclear
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Electrical energy can come from renewable
sources:
 Biomass
 Solar
 Geothermal
-- Wind
-- Hydroelectric
TOPIC 8 – ENERGY PRODUCTION AND THE
ENVIRONMENT
All methods of energy production have their
pros and cons. Read about it in topic 8!
 For example: The burning of fossil fuels creates
are pollution.
 Technology like scrubbers can help reduce the
amount of harmful gases released into the air.
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