Transcript Example Chapter 7 Electricity

Section 1 Electric Charge
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Accumulation of excess electric charge
As you walk across the carpet, electrons are
transferred from the carpet to your shoes
Your shoes become negatively charged
The carpet becomes positively charged
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Charge can be transferred from object to
object, but it cannot be created or destroyed.
Usually the electrons move from place to
place
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“Like” charges repel
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“Unlike” charges attract
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This is why clothes from the dryer stick
together due to the transfer of electrons
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There is an electric field around every electric
charge
Example:
Being shocked when you reach for a doorknob
but do not actually touch it
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Conductors- electrons move through easily
Ex: Metals
Insulator- electrons do not move through this
material easily
Ex: Plastics
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Charging by contact- charge is transferred by
touching or rubbing
Charging by induction- charges are
rearranged on a neutral object due to a
nearby charged object
Section 2 Electric Current
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This is the flow of electrons
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Measured in amperes; amps
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The rate that the electrons move through a
conductor.
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Related to the force that causes electric
charges to flow
Measured in volts; V
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Electric Charge flows from higher voltage to
lower voltage
A.K.A. :
 Potential Difference- the work that must be
done to move a charge from one place to
another
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Closed path that current flows through
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Current will only flow on a closed path
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How much a material opposes the flow of
electrons
Measured in ohms; Ω
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Temperature
Length
Thickness
*When these
increase so does
resistance
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Equation
Current = voltage difference
resistance
or
I= V
R
Calculate the voltage difference in a circuit with
a resistance of 25Ω if the current in the
circuit is 0.5 A.
A current of 0.5 A flows in a 60 W light bulb
when the voltage difference between the ends
of the filament is 120 V. What is the
resistance of the filament?
Section 3 Electrical Energy
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Closed Circuit: Charge can flow uninterrupted
Open Circuit: Charge cannot flow; circuit is
broken
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Switch- used to open and close a circuit
- Ex: Light switch in your home
Schematic Diagram- a diagram that depicts
the construction of an electrical circuit or
apparatus
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The current can only flow through one loop
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Used in flashlights and holiday lights
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These have two or more circuits the current
can move through
Used in houses and automobiles
Useful because unlike series circuits,
individual parts can be turned off without
affecting the entire circuit
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If too much current flows through the wires,
they will overheat and melt which can cause a
fire
To protect against this fuses and circuit
breakers are used
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These contain a small piece of metal that will
melt if it becomes too hot
This causes a break in the circuit which stops
the flow of current
You must replace these with new ones
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Contains a piece of metal that bends when it
overheats
The bending causes a switch to flip which
opens the circuit and stops the current flow
These may be reset by flipping the switch
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How fast electrical energy is converted to
another type of energy
This can be thermal, light, mechanical energy
etc.
Electric power = current X voltage difference
P= I(V)
*Measured in watts; W
*One kilowatt (kW) = 1,000 watts
The current in an electric clothes dryer is 15 A
when it is plugged into a 240 volt outlet. How
much power does the clothes dryer use?
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Measured in kilowatt hours (kWh)
Equation:
Electrical energy = electric power X time
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or
E= Pt
A microwave oven with a power rating of 1,200
W is used for 0.25 h. How much electrical
energy is used by the microwave?