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ELECTRICITY AND MAGNETISMPHYSICAL SCIENCE UNIT 4
WARM UP
Go to Canvas to complete your daily
warmup.
ELECTRIC CHARGE
PARTS OF AN ATOM
•Protons (P+)
• Have a positive electric charge
•Electrons (e-)
• Have a negative electric charge
•Neutrons
• Are neutral
• Have no charge
ELECTRIC CHARGE
• In most atoms, the charges of the protons and electrons
cancel each other out
•Atom has no net charge
•Atoms become charged by: GAINING AND LOSING
ELECTRONS
STATIC ELECTRICITY
•The accumulation of excess electric charges on an
object
LAW OF CONSERVATION OF CHARGE
•Charge may be transferred from object to object,
but it cannot be created or destroyed.
•Sound familiar?
• Law of Conservation of Energy
OPPOSITES ATTRACT
LIKES REPEL
CHARGED ATOMS
• Electric field is generated by electrically charged particles and
time-varying magnetic fields.
• Charges can act on each other even at a distance
STATIC
ELECTRICITY
ACTIVITY
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CONDUCTORS AND INSULATORS
CONDUCTORS
•Materials that allow electrons to
easily move through.
• Examples:
• Metals
INSULATORS
• Materials that do not allow
electrons to easily move through.
• Examples:
• Plastic
• Wood
• Rubber
• Glass
Objects can be charged in several ways…
CHARGING BY CONTACT/FRICTION
•Process of transferring
charge by touching or
rubbing
•Example
• Rubbing your feet on the
carpet and getting static
electricity
CHARGING BY INDUCTION
•Process of rearranging electrons on a neutral object by a
nearby charged object
• Example
• A balloon that has been rubbed on your hair causing someone else’s
arm hair to move
STATIC DISCHARGE
•A transfer of charge through the air between two objects
because of a buildup of static electricity
• Examples
• Lightning
• Spark from touching objects
GROUNDING
•Using a conductor to direct an electric charge to the
ground
• Examples
• Lightning Rod
STATIC ELECTRICITY
•Static Electricity
• the net accumulation of electric charges on an object
•Electric Field
• force exerted by an e- on anything that has an electric charge
• opposite charges attract
• like charges repel
STATIC ELECTRICITY
•Static Discharge
• the movement of electrons to relieve
a separation in charge
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VOLTAGE
•ALWAYS flows from High to
Low voltage
•A voltage difference is the
push that causes charges to
move.
•Measured in volts (V)
RESISTANCE•The tendency for a material to oppose the flow of
electrons
• Changes electrical energy into thermal energy and light
• All materials have some electrical resistance
Copper - low resistance Tungsten - high resistance
RESISTANCE PROPERTIES•Measured in Ohms (Ω)
•Resistance increases with
• Increased length
• Decreased diameter
• Increased heat
Compare resistance to a garden hose!
ELECTRICAL CIRCUITS
•An electrical circuit is a network
consisting of a closed loop,
giving a return path for the
current that flows through it
•Current, voltage, and resistance
all play a role in circuits
ELECTRICAL CIRCUITS
•For charges to flow (to
have current or voltage)
a wire must always be
connected in a closed
path
CIRCUIT COMPONENTS (LABEL IN NOTES)
A - battery C - light bulb
B - switch D - resistor
SERIES CIRCUITS
DEFINITION
• A current that has only one
pathway (or loop) to
follow
PROPERTIES• Current is the same
throughout circuit (Lights are
equal brightness)
• Each device receives a
fraction of the total voltage
(Lights get dimmer as more
lights are added)
• If any part of the circuit is
broken, the current stops
flowing
EXAMPLE
• Some holiday lights
PARALLEL CIRCUITS
DEFINITION
• A current that has two or
more branches (pathways)
to follow
PROPERTIES• Current travels in multiple
paths (One break doesn’t
stop flow)
• Current varies in different
branches; Takes path of
least resistance (“Bigger”
light would be dimmer)
• Each device receives the
total voltage (No change
when lights are added)
EXAMPLE
• The electrical system in a
house
ELECTRIC FUSE AND CIRCUIT BREAKERS
•Electrical Fuses and Circuit Breakers
guard against overheating electric
wires in a circuit
•Contains a small piece of metal that
melts if current becomes too high or
bends when it gets too hot
CIRCUIT BUILDING LAB ACTIVITY
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CIRCUIT BUILDING ONLINE
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OHM’S LAW
•Current = Voltage / Resistance V=Voltage
I=Current
R=Resistance
OHM’S LAW A lightbulb with a resistance of 160 is
plugged into a 120-V outlet. What is the current flowing through the bulb?
GIVEN:
R = 160
V = 120 V
I = ?
WORK:
I = V ÷ R
I = (120 V) ÷ (160 )
I = 0.75 A
I
V
R
ELECTRICAL POWER
THE RATE AT WHICH ELECTRICAL ENERGY IS CONVERTED FROM ONE FORM TO ANOTHER
P = I × V
P: power (W)
I: current (A)
V: potential
difference(V)
ELECTRICAL POWER A calculator has a 0.01-A current flowing through it.
It operates with a potential difference of 9 V. How much power does it use?
GIVEN:
I = 0.01 A
V = 9 V
P = ?
WORK:
P = I · V
P = (0.01 A) (9 V)
P = 0.09 W
I
P
V
ELECTRICAL ENERGY
E = P × tE: energy
(kWh)
P: power (kW)
t: time (h)
ELECTRICAL ENERGY A refrigerator is a major user of electrical power. If it
uses 700 W and runs 10 hours each day, how much energy (in kWh) is used in one day?
GIVEN:
P = 700 W = 0.7
kW
t = 10 h
E = ?
WORK:
E = P · t
E = (0.7 kW) (10 h)
E = 7 kWh
P
E
t
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MAGNETISMAND ITS USES
MAGNETISM
• Force of attraction or
repulsion between unlike or
like poles
•Due to the arrangement of
electrons
•Closely related to electricity
MAGNETIC FORCE
• Interaction between two
magnets
• Increases as distance decreases
• Bring your two magnets
together-what happens?
MAGNETIC POLES
•The regions of a magnet where
the magnetic force exerted by
the magnet is strongest
•North and South
ABOUT MAGNETIC POLES
Like poles repel
Unlike poles attract
A broken magnet creates new
poles!
MAGNETIC FIELD
• Area around a magnet where magnetic forces act
• Field lines show direction of field (N→S)
MAGNETIC FIELD
•Exerts magnetic force
•Surrounds a magnet
•Strongest closer to a
magnet
EARTH’S MAGNETIC FIELD
•A compass needle
•Is a small bar magnet that
can freely rotate
•Always points
NORTH
MAGNETIC DOMAIN
•Groups of atoms with aligned magnetic poles
In a magnetized object, domains are all
aligned
domain
PROPERTIES OF MAGNETIC MATERIALS
• The magnetic field created by each atom exerts a force on nearby
atoms
•Magnetic Materials
• Iron
• Cobalt
• Nickel
• Permanent Magnets
• Made by placing a magnetic material in a strong magnetic field forcing a
large number of magnetic domains to line up
MAGNETIC FIELDS
• Produced by moving charges
• Field around a current-carrying wire
forms a circular pattern around the
wire
• Strength depends on the amount of
current flowing through the wire.
• Increased current = increased magnetic
field
ELECTROMAGNET
•Strong, temporary magnet
formed when current is
passed through a coil of wire
surrounding an iron core
•Acts like a bar magnet when
current is on
PARTS OF AN ELECTROMAGNET
•Battery
•Magnetic field is only present when current is flowing
through the wire coil
•Field strength
•Can be increased by increasing the number of coils
•Can be increased by increasing the current flowing through
wire
ELECTRICITY AND MAGNETISM STATIONS
•You will be called up in small
groups to the stations. When
you are not at a station, you
should be working on the
web tasks at your desk. The
links are on Canvas!
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MAGNETISM USES
GALVANOMETER
•A device that uses an electromagnet to measure electric
current
•Gas gauge-sensor attached to float
SPEAKER
Electrical energy → Mechanical energy
Wire coil moves back &
forth as its magnetic field
interacts with the field of
a fixed magnet
Forced vibration causes
the cone to move
sound
MOTOR
•Electrical energy → mechanical energy
Electromagnet rotates
between the poles of a
fixed magnet
Commutator reverses
the poles of the magnet
ELECTRIC MOTOR• Contains an electromagnet that is free to rotate between the poles
of a permanent, fixed magnet.
• Coil in the electromagnet is connected to the source of current.
ELECTRIC MOTOR• Changing the direction of the current causes the coil in the motor to
keep rotating
• Rotation speed of motors can be controlled
• Vary amount of current
• More current = stronger magnetic field = magnetic force b/w coil and permanent
magnetic increases = coil turns faster
ELECTROMAGNETIC INDUCTION•Producing a current by moving a wire through a
magnetic field
Some microphones
work just like mini-
speakers in reverse
Sound waves cause
coil to move →
current
Dynamic Microphone
Coil
GENERATING ELECTRICITY
•Electricity used in a home comes from a power plant
with huge generators.
•Coils of electromagnets usually connected to a
turbine (a large wheel that rotates when pushed by
water, wind or steam)
ELECTRIC GENERATOR
mechanical energy → electrical energy
Armature is rotated
between magnet
poles
Magnetic field
induces a current in
the wire coil
MOTORGENERATOR
ELECTRIC GENERATOR: HYDROELECTRIC DAM
PE of lake water is
converted to KE
Mechanical KE turns
the generator shaft
which creates
electrical energy
DC & AC
Direct Current (DC)
Current flows in one direction
Dry cells
Alternating Current (AC)
Current reverses its
direction at regular
intervals
Electrical outlets
DIRECT CURRENT (DC)
•Current that flows in only one direction through
a wire
ALTERNATING CURRENT (AC)
•Reverses the direction of the current flow
in a regular way
•In North America: 60 cycles per second =
60 Hz
•Changes directions 120 times each second
TRANSFORMER• Increases or decreases AC voltage
•Primary coil AC produces a magnetic field that
induces AC in the secondary coil
•Voltage ratio = ratio of turns in each coil
TRANSFORMER
• Step-up Transformer
increases the voltage
more turns
power plants
Step-down Transformer
decreases the voltage
fewer turns
household appliances
(hairdryers, etc.)
ELECTRICITY AND MAGNETISM STATIONS
•You will be called up in small
groups to the stations. When
you are not at a station, you
should be working on the
web tasks at your desk. The
links are on Canvas!
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STUDY GUIDES
•Log into Socrative.com (Room: XX7CWRJG)
•Complete the questions. As you do so, fill out your study
guide. You will receive a classwork grade for doing so.
•We will stop at 8:15 to play a review game. Remember,
notes, warmups, and EdPuzzles will be checked
tomorrow. Be sure you have turned in all electricity
classwork.
ELECTRICITY AND MAGNETISM
TEST REVIEW
WHAT ARE THE THREE PARTS OF AN ATOM AND THEIR CHARGES?
AN OBJECT BECOMES CHARGED WHEN IT GAINS/LOSES ___________
WHAT COULD BE THE CHARGES OF THE OBJECTS?
WHAT ARE THE CHARGES OF THE OBJECTS?
WRITE THE FORMULA FOR OHM’S LAW.
SOLVE: FIND THE CURRENT
SOLVE: A CALCULATOR USES 9 V BATTERY & DRAWS 0.1 A OF CURRENT. HOW MUCH POWER DOES IT USE?
•P = I × V
P: power (W)
I: current (A)
V: potential
difference(V)
V=IR P=IV E=PTVOLTAGE=CURRENT X RESISTANCE POWER=CURRENT X VOLTAGE ENERGY=POWER X TIME
•Solve: If a toaster produces 12 ohms of
resistance in a 120-volt circuit, what is the
amount of current in the circuit?
•Solve: A 12 Volt car battery pushes charge
through the headlight circuit resistance of 10
ohms. How much current is passing through the
circuit?
V=IR P=IV E=PTVOLTAGE=CURRENT X RESISTANCE POWER=CURRENT X VOLTAGE ENERGY=POWER X TIME
•Solve: An alarm clock draws 0.5 A of current when
connected to a 120 volt circuit. Calculate its
resistance.
V=IR P=IV E=PTVOLTAGE=CURRENT X RESISTANCE POWER=CURRENT X VOLTAGE ENERGY=POWER X TIME
•Solve: A walkman uses a standard 1.5 V
battery. How much resistance is in the circuit if
it uses a current of 0.01A?
V=IR P=IV E=PTVOLTAGE=CURRENT X RESISTANCE POWER=CURRENT X VOLTAGE ENERGY=POWER X TIME
•An electric heater works by passing a current of
100 A though a coiled metal wire, making it red
hot. If the resistance of the wire is 1.1 ohms, what
voltage must be applied to it?
V=IR P=IV E=PTVOLTAGE=CURRENT X RESISTANCE POWER=CURRENT X VOLTAGE ENERGY=POWER X TIME
DRAW A SERIES CIRCUIT.
•Current flows in one path
• If one light goes out, all
go out
• If lights are added, the
others dim
•Example: Christmas lights
DRAW A PARALLEL CIRCUIT
• Current has multiple paths to
take
•One light going out does not
affect the others
• If lights are added, no change to
others
• Example: House Circuit
LABEL THE FOLLOWING AS EITHER SERIES OR PARALLEL CIRCUIT
1. Has 1 pathway for current to flow
2. Has 2 or more separate branches for current
3. All bulbs are the same brightness
4. Removing 1 light bulb would stop the current flow
5. Removing light bulbs will not affect the other bulbs
AC (ALTERNATING) VS. DC (DIRECT) CURRENT
•DC: Current flows one
direction
• Ex. Electronic devices
•AC: Current changes direction
• Ex. Houses
WHAT IS A CONDUCTOR? WHAT IS AN INSULATOR?
•Conductor: Allows electrons to flow
•Ex. Metals
•Insulator: Does not allow the flow of electrons
•Ex. Plastic, rubber, glass
A MAGNET HAS A ________ POLE AND A _________POLE
LABEL THE MAGNETS BELOW SO THERE WOULD BE NO ATTRACTION BETWEEN THEM.
IF YOU BREAK A MAGNET, WHAT WILL HAPPEN?
•It will form two new magnets!
HOW CAN YOU INCREASE THE STRENGTH OF AN ELECTROMAGNET WITH THE COIL?
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•Test Code: EMTest4