Can RollingHold a balloon near a can, observe

Now charge one side of balloon and hold near can, observe

Rub a can the same way you did the balloon, hold near a neighbor's can, observe

Experiment with how far you can hold balloon away from can to affect it

Write some of your observations on a new notes page. Draw a diagram of the balloon and can to explain what you think is happening

Electricity and Electricity and MagnetismMagnetism

TUESDAY

WARM UP

Think back to our unit on atomic structure:

Sometimes we refer to an object as having a charge, what kinds of charges are there and what parts of the atom contain these charges?

The AtomThe Atom

• Electrically neutralElectrically neutral• Equal protons + Equal protons +

electronselectrons• ProtonsProtons• ElectronsElectrons• NeutronsNeutrons

Charge Charge – Positive, Negative or NeutralPositive, Negative or Neutral

We Cannot see, weigh or We Cannot see, weigh or define a chargedefine a charge– But, we can observe its But, we can observe its

behavior on other behavior on other particles (objects)particles (objects)

So how DID that balloon So how DID that balloon stick to the wall???stick to the wall???

Charges Charges

• Remember, only electrons are free to Remember, only electrons are free to move about!move about!

• Lose Lose electrons = object has electrons = object has positive chargepositive charge

• GainGain electrons = object has negative electrons = object has negative chargecharge

• Atoms that have a (+) or (-) charge are Atoms that have a (+) or (-) charge are called called ionsions

+ + - - - -

+ + + + - -

Hey! I could have sworn I had 2

more electrons?!?

Like Charges Repel, Like Charges Repel, Opposite AttractOpposite Attract

Warm Up

1. Draw the charges on a ballostatic electricity.

2. Indicate whether of the following objects would be negatively charged or positively charged

3. Which objects above would be attracted to each other? Which would be repelled?

Static Electricity

Electric Force What is it? Where is it? Examples

Static ElectricityStatic Electricity

• Static Electricity is:Static Electricity is:• the transfer of the transfer of electronselectrons from one object from one object

to another without further movementto another without further movement• the build-up of electric charges on an the build-up of electric charges on an

object object

Why is it called Why is it called STATICSTATIC? - static means ? - static means stationary....stationary....

But wait! It doesn't stay there forever....

Static Discharge – the rapid transfer of the built up electrons from one object

to another without build-up

Grounding – the discharge of electrons from a charged object to another object on the earth

How might this affect you? Where do we see grounding in our lives?

Air and Static ElectricityAir and Static Electricity

• Charged objects usually lose their Charged objects usually lose their charge to water molecules in the aircharge to water molecules in the air

• When have you noticed static When have you noticed static electricity more often?electricity more often?

Static Electricity

There are 3 ways static electricity is charged to an object

1. Friction

2. Induction

3. Conduction

Charging by Friction

The friction force of rubbing two materials together is used to rip electrons off of the atoms making up a material.

Ex: rubbing balloon on your clothes. Dragging your feet across the carpetOther examples?

Charging by Induction

Charges within an object rearrange themselves due to a charged object being nearby.

before after

Charging by Conduction

Charges move from one charged object to another through direct contact between the objects.

Ex: Van de Graff machine

Insulators and Conductors

Not all materials allow charges to move through them.

Insulators: Materials that block the flow of electrons through a material

Conductors: Materials that allow electrons to move easily through them

Why is this important when we are studying electricity?

Electric FieldElectric Field• An An electric fieldelectric field extends extends

outward through space from outward through space from every charged particle every charged particle

• As the distance from the As the distance from the charged particle increases, charged particle increases, the strength of the electric the strength of the electric field decreases field decreases

This makes sense!This makes sense!

Electric Field Greatest Where Electric Field Greatest Where Lines are Close to Each OtherLines are Close to Each Other

Detecting Electric ChargeDetecting Electric Charge

• Electroscope – Electroscope – detects electric detects electric chargecharge

• Leaves hang Leaves hang straight – no straight – no chargecharge

• Leaves spread – Leaves spread – electric charge electric charge presentpresent

Electroscope WarmupElectroscope Warmup

Describe what is happening to the electrons when the balloon was brought near the ball on the electroscope.

This is an example of charging by which method?

Sometimes electroscopes don't work well when the air is humid (damp). Why might this be?

The Flow of ElectricityThe Flow of Electricity

• Work must be done to move a charged Work must be done to move a charged particle between two pointsparticle between two points– How is static electricity different?How is static electricity different?– How can we keep charges moving to make How can we keep charges moving to make

current electricitycurrent electricity??• Batteries, electric generators, and photo Batteries, electric generators, and photo

cells supply the energy needed to keep cells supply the energy needed to keep charges movingcharges moving

Current ElectricityCurrent Electricity

• Electrons are moving, so what kind of energy do they have?

• As the electrons move through the material in the circuit, they collide with the atoms in the material. So energy is passed on.

Current vs. Static Electricity

• Static Electricity– Build up and one time discharge of all

e-, due to electric force– Examples: Lightning, getting shocked,

etc.

• Current Electricity– Continuous flow of electrons, due to

electric force– Examples: light bulbs, cell phones, etc.

Current Electricity

• Resistance– Material that gets in the way of the electrons,

slowing them down.– SI unit: Ohm Ω

• Current– Amount of electrons flowing through circuit.– SI unit: Ampere (A)

• Voltage (Potential Difference)– Amount of charge build up and separation– SI unit: Volt (V)

Electric CircuitsElectric Circuits

• A A Circuit is a Circuit is a complete complete pathpath when a when a wire is wire is connected to connected to the terminals the terminals of a sourceof a source

Terminals

Types of Circuits

• Series Circuits– One path for the electrons

to flow.– If one part of the circuit

goes out, all other parts go out as well

• Parallel Circuits– Multiple paths for the

electrons to flow.– If one part of the circuit

goes out, the other parts are not affected

Series CircuitSeries Circuit

• DisadvantageDisadvantage: if there is : if there is a break anywhere in the a break anywhere in the circuit, the entire circuit circuit, the entire circuit is open and no current is open and no current can flowcan flow

– EX: EX: Christmas tree Christmas tree lightslights

Parallel CircuitParallel Circuit

• If there is a break If there is a break in one branch, the in one branch, the electrons and electrons and current can still current can still flow through the flow through the other branchesother branches

• Our Homes are Our Homes are wired with Parallel wired with Parallel CircuitsCircuits

Types of Circuits

• Identify the following as series or parallel.

Ohm’s Law

• Ohm’s Law– As more “stuff”

(resistance) gets in the way, there will be less flowing electrons (current)

– As there is more charge build up and separation (Voltage), there can be more electron flow

– V = I R

Current vs Resistance

0

5

10

15

20

25

30

0 5 10 15

Resistance (Ohms)

Cu

rre

nt

(Am

pe

res

)

Ohm’s LawOhm’s Law

• V= I*RV= I*R• Current (l) = Current (l) = amperesamperes• Voltage (V) = Voltage (V) = VoltsVolts• Resistance (R) = Resistance (R) = OhmsOhms

Electric PowerElectric Power

• The measure of the rate at which The measure of the rate at which electric energy does work or electric energy does work or provides energy (how quickly it provides energy (how quickly it pushes charges through a circuit)pushes charges through a circuit)

• Power = Current x VoltagePower = Current x Voltage• P = V * IP = V * I

– Large quantities measured in Large quantities measured in kilowatts (Ex: your home)kilowatts (Ex: your home)

Practice Problem 1Practice Problem 1

• Calculate the voltage in a circuit Calculate the voltage in a circuit with a resistance of 25 with a resistance of 25 if the if the current in the circuit is 0.5 A.current in the circuit is 0.5 A.

• V=I*RV=I*R

Plug in the numbersPlug in the numbers

V=.5 * 25V=.5 * 25

V= 12.5 VV= 12.5 V

Practice Problem 2Practice Problem 2

• A current of 0.5 A flows in a 60-W A current of 0.5 A flows in a 60-W light bulb when the voltage light bulb when the voltage between the ends of the filament is between the ends of the filament is 120 V. What is the resistance of 120 V. What is the resistance of the filament?the filament?

• V= I*R V= I*R

120 = .5 R120 = .5 R

R = 240 OhmsR = 240 Ohms

Practice Problem 3Practice Problem 3

• A toaster oven is plugged into an A toaster oven is plugged into an outlet that provides a voltage outlet that provides a voltage difference of 120 V. What power difference of 120 V. What power does the oven use if the current is does the oven use if the current is 10 A?10 A?

• P = V*IP = V*I

P = 120 * 10P = 120 * 10

P = 1200 WattsP = 1200 Watts

Practice Problem 4Practice Problem 4

Calculate the current flowing into a Calculate the current flowing into a desktop computer plugged into a desktop computer plugged into a 120-V outlet if the power used is 120-V outlet if the power used is 180 W.180 W.

• P = V*IP = V*I

180 = 120*I180 = 120*I

I = 1.5 AmpsI = 1.5 Amps

Electrical EnergyElectrical Energy

• Electric companies charge a certain Electric companies charge a certain amt for electricityamt for electricity

• The bill is based on how much The bill is based on how much energy is used in the householdenergy is used in the household

• Electric meter records this amount Electric meter records this amount of energyof energy

MagnetismMagnetism

Magnets....How long have we known about magnets??....

MagnetismMagnetism

• Refers to the unseen forces of Refers to the unseen forces of attraction and repulsion between of attraction and repulsion between of magnetsmagnets

• Magnetic Force – magnets exert Magnetic Force – magnets exert force on each otherforce on each other– The closer they are, the stronger the The closer they are, the stronger the

forceforce• A magnet is surrounded by a A magnet is surrounded by a

magnetic field.magnetic field.

Magnetic PolesMagnetic Poles

• Where the Where the magnetic force magnetic force exerted by the exerted by the magnet is the magnet is the strongeststrongest

• North PoleNorth Pole• South PoleSouth Pole• Bar magnet – N + Bar magnet – N +

S poles oppositeS poles opposite

How Do Magnets Interact?How Do Magnets Interact?

• Like poles repelLike poles repel• Opposite poles Opposite poles

attractattract• When 2 magnets When 2 magnets

are brought close to are brought close to each other, their each other, their magnetic fields magnetic fields combine to produce combine to produce a new magnetic a new magnetic field.field.

Magnetic FieldMagnetic Field• Exerts a force on Exerts a force on

other magnets other magnets and objects made and objects made of magnetic of magnetic materialsmaterials

• Represented by Represented by magnetic field magnetic field lineslines

• We detect a We detect a magnetic field magnetic field with a compasswith a compass

Magnetic DomainMagnetic Domain

• Domain before Domain before magnetismmagnetism

• Domain after Domain after magnetismmagnetism

Magnetic MaterialsMagnetic Materials

• Iron - BestIron - Best• CobaltCobalt• NickelNickel

                                                                              

            

Materials Not MagneticMaterials Not Magnetic

• WoodWood• GlassGlass• PlasticPlastic

Can a Magnet Lose Its Can a Magnet Lose Its Magnetism?Magnetism?

• Heated atoms can Heated atoms can begin to move begin to move fast enough to fast enough to jostle alignment of jostle alignment of domainsdomains

Can a Broken Magnet Still Have Can a Broken Magnet Still Have a North and South Pole?a North and South Pole?

• YesYes• Every magnet is Every magnet is

made of many made of many aligned smaller aligned smaller magnetsmagnets

ElectromagnetElectromagnet• Temporary Temporary

magnet made by magnet made by wrapping a wire wrapping a wire coil carrying a coil carrying a current around an current around an iron coreiron core

• The electron flow The electron flow (current (current electricity) creates electricity) creates a magnetic fielda magnetic field