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Electricity
Chapter 7 Section 1
Electric Charge
Sections
• 1. Electric Charge slides 3 - 35
• 2. Electric Current slides 36 - 67
• 3. Electrical Energy slides 68 - 96
Electric Charge
• The center of an atom is made of protons (+)
and neutrons (no charge).
Electric Charge
• The center of an atom is made of protons (+)
and neutrons (no charge).
• Electrons (-) move around the center of the
atom.
Electric Charge
• The amount of +
Charge on a proton =
The amount of –
Charge on an electron.
Electric Charge
• The amount of +
Charge on a proton =
The amount of –
Charge on an electron.
• Each atom has the
same number of
protons & electrons
making them
electrically neutral.
Electricity
• Atoms have no charge.
Electricity
• Atoms have no charge.
• - ion if it gains
electrons
Electricity
• Atoms have no charge.
• - ion if it gains
electrons
• + ion if it loses
electrons
Electricity
• Atoms have no charge.
• - ion if it gains
electrons
• + ion if it loses
electrons
• Electrons can move
from atom to atom or
from object to object.
Static Electricity
• Is the buildup of charges on an object.
Static Electricity
• Is the buildup of charges on an object.
• When there is static electricity, the electric
charges are not balanced.
Static Electricity
• Is the buildup of charges on an object.
• When there is static electricity, the electric
charges are not balanced.
• The Law of Conservation of charge states
that charge can be transferred from object to
object but it cannot be created or destroyed.
Electricity
• Opposite charges
attract
+
-
• Like charges repel
+
+
-
-
Electricity
• The electric force between charged objects
depends on how far apart they are.
Electricity
• The electric force between charged objects
depends on how far apart they are.
• The force decreases the farther apart the
charges are.
Electricity
• The electric force between charged objects
depends on how far apart they are.
• The force decreases the farther apart the
charges are.
• The electric force also depends upon the
amount of charge on the objects.
Electricity
• The electric force between charged objects
depends on how far apart they are.
• The force decreases the farther apart the
charges are.
• The electric force also depends upon the
amount of charge on the objects.
• More charge = More force
Electric Field
• Area around every electric charge that exerts
a force.
+
-
• Movement of a positive charge in electric
fields.
Electric & Gravitational Force
• Electric forces are stronger than gravity.
Electric & Gravitational Force
• Electric forces are stronger than gravity.
• Atoms are held together by electric forces.
Electric & Gravitational Force
• Electric forces are stronger than gravity.
• Atoms are held together by electric forces.
• These forces cause chemical bonds to make
a new substance.
Electric & Gravitational Force
• Electric forces are stronger than gravity.
• Atoms are held together by electric forces.
• These forces cause chemical bonds to make
a new substance.
• Electric forces between atoms are greater
than the gravitational forces between atoms.
Electric & Gravitational Force
• Electric forces are stronger than gravity.
• Atoms are held together by electric forces.
• These forces cause chemical bonds to make
a new substance.
• Electric forces between atoms are greater
than the gravitational forces between atoms.
• Electric forces between most objects are
less than the gravitational forces between
them because most objects are elec. neutral.
Conductors & Insulators
• Electrons move more easily in conductors.
Conductors & Insulators
• Electrons move more easily in conductors.
Ex. Metals such as copper
• Insulators do not allow electrons to move as
easily. Ex. Plastic, wood rubber and glass
Charging Objects
• Charging by contact- transferring charges by
touching or rubbing ex. Clothes in a dryer
Charging Objects
• Charging by contact- transferring charges by
touching or rubbing ex. Clothes in a dryer
• Charging by induction- charged object
rearranges the electrons on a nearby neutral
object.
Lightning
• Large static discharge between clouds and
the ground that causes atoms & molecules to
light up.
Lightning
• Large static discharge between clouds and
the ground that causes atoms & molecules to
light up.
• Thunder- Electric energy in a lightning bolt
rips electrons off atoms in the air causing
great amounts of heat, up to 25,000 °C.
Lightning
• Large static discharge between clouds and
the ground that causes atoms & molecules to
light up.
• Thunder- Electric energy in a lightning bolt
rips electrons off atoms in the air causing
great amounts of heat, up to 25,000 °C.
• The heat makes the air around the lightning
bolt move faster creating sound waves.
Grounding
• Grounding avoids damage by providing a
path for electric charge to move to earth.
Electroscope
• Can detect when an
object has an electric
charge.
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Electroscope
• Can detect when an
object has an electric
charge.
• The metal rod is a
conductor.
Electroscope
• Can detect when an
object has an electric
charge.
• The metal rod is a
conductor.
• When the leaves have
a charge they repel
each other and spread
apart.
Electric Current
Chp 7 Section 2
Electric Current
• The net movement of electric charges in one
direction.
Electric Current
• The net movement of electric charges in one
direction.
• Measured in units called amperes or amps.
Electric Current
• The net movement of electric charges in one
direction.
• Measured in units called amperes or amps.
• Symbol for amperes is A.
Electric Current
• The net movement of electric charges in one
direction.
• Measured in units called amperes or amps.
• Symbol for amperes is A.
• Measures the electrons that flow past one
point.
Electric Current
• The net movement of electric charges in one
direction.
• Measured in units called amperes or amps.
• Symbol for amperes is A.
• Measures the electrons that flow past one
point.
• 1 A = 6,250 million billion electrons moving
past a point every second.
Voltage
• The electric force that makes charges move.
Voltage
• The electric force that makes charges move.
• Voltage is like the force that acts on water in
a pipe.
Voltage
• The electric force that makes charges move.
• Voltage is like the force that acts on water in
a pipe.
• Water flows from higher pressure to lower;
likewise, electric charge flows from higher
voltage to lower voltage.
Voltage difference
• Related to the force that makes electric
charges flow.
Voltage difference
• Related to the force that makes electric
charges flow.
• Measured in units called volts (V).
Electric Circuit
• Closed loop-like path
that current must
follow.
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Electric Circuit
• Closed loop-like path
that current must
follow.
• If the circuit is broken,
current will not flow &
bulb will not light.
Batteries
• Provide the voltage difference that keeps
electric current flowing in a circuit.
Batteries
• Provide the voltage difference that keeps
electric current flowing in a circuit.
• The positive & negative ends are called
terminals.
Batteries
• Provide the voltage difference that keeps
electric current flowing in a circuit.
• The positive & negative ends are called
terminals.
• When a closed path connects the terminals,
current will flow.
Types of Electric Cells
• Electrochemical- electrons move b/w
different metals in an electrolyte solution
– A. dry cell - use paste – flashlight battery
– B. wet cell – use liquid – car battery
Types of Electric Cells
• Electrochemical- electrons move b/w
different metals in an electrolyte solution
– A. dry cell - use paste – flashlight battery
– B. wet cell – use liquid – car battery
• Photovoltaic – electrons move when light hits
a material – calculators, solar panels
Types of Electric Cells
• Electrochemical- electrons move b/w
different metals in an electrolyte solution
– A. dry cell - use paste – flashlight battery
– B. wet cell – use liquid – car battery
• Photovoltaic – electrons move when light hits
a material – calculators, solar panels
• Thermoelectric – electrons move across two
metals joined together & held at different
temperatures – thermostats for ovens
Types of Electric Cells
• Electrochemical- electrons move b/w different
metals in an electrolyte solution
– A. dry cell - use paste – flashlight battery
– B. wet cell – use liquid – car battery
• Photovoltaic – electrons move when light hits a
material – calculators, solar panels
• Thermoelectric – electrons move across two metals
joined together & held at different temperatures –
thermostats for ovens
• Piezoelectric – electrons move when opposite
surfaces of crystals become charged under
pressure – mikes, keyboards
Electrical outlets
• Also give a voltage difference, usually higher
than a battery, such as 120 V or 240 V for
large appliances.
Resistance
• The tendency for a material to oppose the
flow of electrons, changing electric energy
into heat and light
Resistance
• The tendency for a material to oppose the
flow of electrons, changing electric energy
into heat and light.
• Electrons flowing through the wire filament of
a light bulb bump into metal atoms heating
the filament until it glows lighting up…electric
to thermal to radiant energy.
Resistance
• The tendency for a material to oppose the
flow of electrons, changing electric energy
into heat and light.
• Electrons flowing through the wire filament of
a light bulb bump into metal atoms heating
the filament until it glows lighting up.
• Resistance turns electric energy into heat &
light.
Resistance
• is measured in units called ohms (Ω) or the
Greek letter omega.
Resistance
• is measured in units called ohms (Ω) or the
Greek letter omega.
• Temperature, length, & thickness of a
material can affect its electrical resistance.
Resistance
• is measured in units called ohms (Ω) or the
Greek letter omega.
• Temperature, length, & thickness of a
material can affect its electrical resistance.
• Hotter, longer & thinner – more Ω
a simple circuit requires
1. Source of voltage difference i.e. Battery
2. Device with resistance i.e. light bulb
3. Conductors i.e. wires connecting all three so
that current can flow.
Ohm’s law
• States that the current in a circuit equals the
voltage difference divided by the resistance.
Ohm’s law
• States that the current in a circuit equals the
voltage difference divided by the resistance.
• If I stands for electric current, Ohm’s law can
be written as :
current (in amps) = voltage difference
resistance (in Ω)
I = V/ R or R = V/I
Problem
• Suppose a current of 0.5 A flows in a 75-W
light bulb. The voltage difference b/w the
ends of the filament is 120 V. Find the
resistance of the filament.
Problem
• Suppose a current of 0.5 A flows in a 75-W
light bulb. The voltage difference b/w the
ends of the filament is 120 V. Find the
resistance of the filament.
• R = V/I = 120/0.5 = 240
• The resistance is 240 Ω.
Electrical Energy
Chapter 7 section 3
Electrical energy
• When you turn a hair dryer on, you close a
circuit. EE turns into thermal energy & ME.
– Voltage difference –
– Resistance –
– Conductor -
Electrical energy
• When you turn a hair dryer on, you close a
circuit. EE turns into thermal energy & ME.
– Voltage difference – outlet
– Resistance – hair dryer
– Conductor - wires
Kinds of Circuits
• Series –
• Parallel -
Kinds of Circuits
• Series – current has only one loop to flow
through i.e. flashlights
• Parallel -
Kinds of Circuits
• Series – current has only one loop to flow
through i.e. flashlights, some Christmas
lights
• Parallel – have at least two circuits for
current to move through i.e. houses
Circuits
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Circuits
SERIES
PARALLEL
Parallel Circuits
• Break up current lowering resistance.
Parallel Circuits
• Break up current lowering resistance.
• More current flows through paths with less
resistance.
Parallel Circuits
• Break up current lowering resistance.
• More current flows through paths with less
resistance.
• Houses, cars and most electrical systems
use parallel systems.
Household Circuits
Household Circuits
• There is a main switch
& a circuit breaker or
fuse box.
Household Circuits
• There is a main switch
& a circuit breaker or
fuse box.
• Parallel circuits branch
out from the circuit
breaker or fuse box.
Household Circuits
• There is a main switch
& a circuit breaker or
fuse box.
• Parallel circuits branch
out from the circuit
breaker or fuse box.
• The circuits run to wall
outlets, appliances, &
lights.
Fuses
• Many appliances use current from the same
circuit causing more heat in the wires.
Fuses
• Many appliances use current from the same
circuit causing more heat in the wires. To
keep wires from causing a fire, household
circuit include a fuse or circuit breaker.
Fuses
• Many appliances use current from the same
circuit causing more heat in the wires. To
keep wires from causing a fire, household
circuit include a fuse or circuit breaker.
• A fuse is a small glass tube with a piece of
metal inside that melts if the current is too
high breaking the circuit.
Fuses
• Many appliances use current from the same
circuit causing more heat in the wires. To keep
wires from causing a fire, household circuit
include a fuse or circuit breaker.
• A fuse is a small glass tube with a piece of
metal inside that melts if the current is too high
breaking the circuit.
• To restore current, the fuse must be replaced.
Fuses
• Using too many appliances at once is the
main cause for a blown fuse.
• You should turn off or unplug some
appliances before changing the fuse.
Circuit Breaker
• Switching device that prevents circuits from
overheating by opening the circuit if the
current is too high.
Circuit Breaker
• Switching device that prevents circuits from
overheating by opening the circuit if the
current is too high.
• You can reset the breaker by flipping the
breaker box back to its original position but
you should turn off or unplug some of the
appliances first.
Electric Power
• Rate at which electrical energy is changed
into another form of energy.
Electric Power
• Rate at which electrical energy is changed
into another form of energy.
• Different appliances use different amounts of
energy and are usually marked with a power
rating.
Electric Power
• Rate at which electrical energy is changed
into another form of energy.
• Different appliances use different amounts of
energy and are usually marked with a power
rating.
• Electric power (watts) = current (amps) X
voltage difference (V) or P = IV
• Power is usually measured in kilowatts (kW)
Electric energy calculation
• Electrical energy (kW) =
electric power (kW) X time (hours)
or E = Pt
A 100 W light bulb left on for 5 h uses:
E = Pt = (0.1kW) (5h) = 0.5 kWh
If the power company charges 10 cents per
kW, the cost of using the light would be 5
cents.
Cost of using Home Appliances
Hair dryer
•
•
•
•
•
Power rating 1,000
Hours/day 0.25
Kwh /month 7.5
Cost / kWh $0.09
Monthly cost $0.68
Stereo
Color TV
100
2.0
6.0
$0.09
$0.54
200
4.0
24.0
$0.09
$2.16
Electric Fuse
Circuit Breaker
contains
contains
that
that
when
And makes the current
when
Electric Fuse
Circuit Breaker
contains
contains
A piece of metal
that
that
Switches the circuit off
Can melt
when
when
It gets too hot
And makes the current
STOP