electricity and magnetism - ms. farris' science class!...properties of magnetic materials...

ELECTRICITY AND MAGNETISMPHYSICAL SCIENCE UNIT 4

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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