Download Chapter 13 Electricity

1. Static electricity is a part of life.
Can you name at least five
examples of static electricity
that occur in your home?
2. Fabric softeners are commonly
used today because they
eliminate static cling. Explain
why clothes in the dryer get
static cling.
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3. Why can walking across a
carpeted room be a shocking
experience?
4. Magnets have both north and
south poles. While like poles
repel each other, opposite poles
attract each other. Explain the
parallelism between magnetism
and electric charge.
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Electricity
Electric Charge
and Force
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Electric Charge
• Electrical property of matter
• Creates a force between objects
•
Positive or Negative
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Electric Charge
• Opposite
charges
• Attract
• Like charges
• Repel
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Electrical Charge
• Depends on the imbalance of
electrons and protons
o Protons
= positive
o Electrons = negative
o Neutron = neutral
• Leads to a net charge
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Coulomb
• SI unit for charge
• Proton = +1.6 x 10-19 C
-19
• Electron = -1.6 x 10 C
• Charges are equal and opposite
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Flow of Charge
• Conductor
o Material
• Insulator
that
o Material
transfers
charge easily
that
does not
transfers
charge easily
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Charging by Contact
• Electrons move from the rod to the
doorknob
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Charging by Contact
• Transfer of
electrons
• Gives the
doorknob a
negative
charge
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Induced Charges
• Induces a positive charge near the rod
• Induces a negative charge away from
the rod
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Induced Charges
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Charging by Friction
• When rubbed together
electrons can be transferred
from one material to the other
• material that gets the electrons
becomes negatively charged
• material that loses the electrons
becomes positively charged
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Electric Force
• The force of attraction or repulsion
between objects
• Due to charge
• Without electric force life would
be impossible
• Depends on charge and distance
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Electric Force
• Proportional to the product of
the charges
• Inversely proportional to the
distance between them squared
• Equation: F = q1 q2 /[4peo r2 ]
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Electric Field
• Produced around charged
particles
• Other charged objects around
will experience an electric force
• Electric force acts through
electric fields
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Point Charges
• Electric field
lines point in
the direction of
the electric
force on a
positive charge
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Point Charges
• Positive is
attracted to
negative
• Electric Field
lines point
inward
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Electric Field Lines
• Show direction
of electric force
• Also show
relative
strength
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Electric Fields
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Electric Fields
In the figure shown,
why do only half of the
lines originating from the
positive charge terminate
on the negative charge?
Because the positive charge is twice
as great as the negative charge.
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Electric Force
• varies depending on
• charge and distance
between charged objects
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Electrical Potential Energy
• Potential energy of charged
object
• Due to its position in electric
field
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Electrical
Potential
Energy
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Potential Difference
• Change in the electrical
potential energy per unit charge
• Measured in Joule / Coulomb
• 1 J/C = 1 volt or 1V or voltage
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Volts
• Measure of potential
difference
• Terminals of a battery have a
potential difference
• Cell (battery)
o Source
of current
o Voltage across the terminals
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Dry Cell and Car
Battery
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Batteries
• Typically have one positive
and one negative terminal.
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Current
• Voltage sets charges in motion
• Current = Rate of electric
charges moving through a
conductor
1 C/s = 1 ampere or 1 amp
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Electric Current
• Produced when charges are
accelerated by an electric
field
• Charges move to a position
of potential energy that is
lower
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Electrical Resistance
• What is the voltage
from the wall?
o 120 V
• What is the power
of a bulb?
40W, 60W, 100W
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Electrical Resistance
• Causes changes in current
• Caused by internal friction
• Slows the movement of charges
through collisions
• Collisions can cause material to
heat up
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Electrical Resistance
(Ohm’s Law)
• Resistance = voltage/current
•R=V/I
•=V/A
•  = Ohm
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Resistance
• A set of electric trains is
powered by a 9 V battery. What
is the resistance of the trains if
they draw 3.0 A of current?
• Answer: 3 
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Resistance
• A battery-operated CD player
uses 12 V from the wall
socket and draws a current
of 2.5 A. Calculate the
resistance of the CD player.
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Resistance
• There is a potential
difference of 12 V across a
resistor with 0.25 A of current
in it. The resistance of the
resistor is
• Answer: 48
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Ohms Law
• A light bulb has a resistance
of 12 . It is attached to a
battery that has a voltage of
24 V. Calculate the current
in the light bulb.
• Answer: 2 A
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Current
• A resistor has a resistance of
280. How much current is
in the resistor if there is a
potential difference of 120 V
across the resistor?
• Answer: 0.43 A
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Series Circuits
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Series Circuits
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Parallel Circuits
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Parallel Circuits
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Electric Energy
• Energy associated with
electrical charges
• Whether moving or at rest
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Electrical Power
• Rate at which electrical energy
is used in a circuit
• power = current x voltage
• P = IV
• 1 Watt = 1 Amp x 1 Volt
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• A color television draws about
2.5 A when it is connected to a
120 V outlet. Assuming
electrical energy costs $0.060
per kWh, what is the cost of
running the television for
exactly 8 hours?
• Answer: $0.14
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8.
• A flashlight bulb with a potential
difference of 4.5 V across its
filament has a power output of
8.0 W. How much current is in
the bulb filament?
• Answer: 1.8 A
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Household Circuits
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• 7. What is the potential
difference across a resistor that
dissipates 5.00 W of power and
has a current of 5.0 A?
• Answer: 1.00 V
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11.
• If a lamp is measured to have a
resistance of 120- when it
operates at a power of 120 W,
what is the potential difference
across the lamp?
• Answer: 120 V
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12.
• A microwave draws 5.0 A when
it is connected to a 120 V outlet.
If electrical energy cost
$0.090/kWh, what is the cost of
running the microwave for
exactly 6 hours?
• Answer: $0.32
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13.
• What happens to the overall
resistance of a circuit when too
many appliances are connected
across a 120 V outlet?
• Answer: Resistance is
decreased.
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11.
• An electric toaster has a power
rating of 1100 W at 110 V. What
is the resistance of the heating
coil?
• Answer: 11
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13.
• A device that protects a
circuit from current overload
is called a(n)
• Answer: circuit breaker.
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14.
• What is charging by contact?
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16.
• A 180-ohm resistor has 0.10
A of current in it. What is the
potential difference across
the resistor?
• Answer: 18 V
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Study Guide
Attraction, repulsion
• Electric force
• Batteries
• Current, potential
• Resistance
• Ohm’s law: V=IR
• Power, P = VI
• Circuits, parallel,
series
• Charge/ing,
• Electric fields
• Conductor,
insulator
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