grade 9 science unit 3: electricity -...
TRANSCRIPT
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Grade 9 Science
Unit 3: Electricity
Chapter 8: Ohm’s law describes the relationship of current, voltage, and resistance.
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Electric Potential Energy
•Stored electrical energy•Ex. A battery has stored electrical energy because the electrons have the ability to do work after they leave the battery.
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Electrical Potential Difference
•The change in potential energy per coulomb of charge.
•Also called voltage•Measured in volts (V)•Measured using a voltmeter
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Electric Charge
•A building up at the negative terminal of a cell/battery which then flows from this terminal as negative charges repel one another.
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Ele
ctr
ic C
urr
ent
Flo
w
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Electric Circuit
•A complete pathway that allows electrons to flow.
•Will transform electrical energy into other forms of energy.
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Sources of Electrical Energy:Source Staring Energy Converts to…
Friction Rubbing
ELECTRICAL ENERGY
Piezoelectriccrystals
Pressure
Photo-electrochemical cells (solar cells)
Solar/ light
Thermocouples Heat
Generators Mechanical
Cells/ Batteries Chemical
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Electric Current
•The amount of charge passing a given point in a conductor per second.
•Measured in amperes (A)•Measured using an ammeter
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Current Electricity
•The continuous flow of charge in a complete circuit.
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Circuit
Diagrams
See symbols on page 262.
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Electrical Resistance
•Slows down the flow of electrons and transforms electrical energy.
•Measured in ohm’s (Ω)•The ratio of the voltage to the current.
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Factors that affect the amount of resistance in a wire are:
1. Length
2. Diameter (thickness)
3. Type
4. Temperature
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Long, thin, tungsten wire
Short, thick, copper wire
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Ohm’s Law
•The mathematical relationship comparing voltage (V), current (I) and resistance (R)
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Ohm’s Law
V
RI
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Ohm
’s L
aw Complete
the practice problems on pg. 273-5
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Resistors
•Used to control current or potential
difference in
a circuit.
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Core
Lab A
cti
vit
y
Resi
stance a
nd
Ohm
’s L
aw
Pages
278-9