ELECTRICITYELECTRICITY

Electric ChargeElectric Charge Atoms are made up of 3 particlesAtoms are made up of 3 particles

– NeutronsNeutrons have a have a neutralneutral charge. charge.– ProtonsProtons have a have a positivepositive charge. charge.– ElectronsElectrons have a have a negativenegative charge.charge.

An atom is electrically neutral if An atom is electrically neutral if the number of electrons the number of electrons EQUALSEQUALS the number of protonsthe number of protons

However, atoms sometimes However, atoms sometimes LOSE or GAIN electrons.LOSE or GAIN electrons.

When excess (or extra) electrons When excess (or extra) electrons are stored, an overall NEGATIVE are stored, an overall NEGATIVE (-) charge is achieved(-) charge is achieved

“Electrons” clip

ChargesCharges Handy rule : Opposites attractHandy rule : Opposites attract

And likes repel

Electric fieldsElectric fields

Every electric charge is surrounded by an Every electric charge is surrounded by an electric field which can exert a force on electric field which can exert a force on objects which come into it.objects which come into it.

These fields can push or pull over distances

2 types of electricity2 types of electricityStatic electricityStatic electricityElectric currentElectric current

Static electricityStatic electricity is an accumulation is an accumulation of electric charges on an object.of electric charges on an object.

- transferred

Negative ChargeNeutral Charge

Charging objectsCharging objects

Objects can become charged by a variety of Objects can become charged by a variety of methodsmethods

2 ways are 2 ways are – Charging by CONTACTCharging by CONTACT– Charging by INDUCTIONCharging by INDUCTION

Charging by ContactCharging by Contact Objects touch or rub Objects touch or rub

against each other against each other (contact)(contact) and charge is and charge is transferredtransferred

Charging by InductionCharging by Induction

Occurs when a Occurs when a charged object is charged object is brought near a brought near a neutral object. The neutral object. The charges in the charges in the neutral object neutral object rearrange rearrange themselves and themselves and present the illusion present the illusion of a charge.of a charge.

Once objects are charged, they can then Once objects are charged, they can then transfer their charge…sometimes, suddenly, in transfer their charge…sometimes, suddenly, in what is called a STATIC DISCHARGE.what is called a STATIC DISCHARGE.

“Balloons on the Wall” clip

Conductors and InsulatorsConductors and InsulatorsConductors = materials which allow excess electrons to easily move through them.

Examples : metals, water

The Earth also functions as a conductor.

Conductors and InsulatorsConductors and Insulators

Insulator = a material that doesn’t allow electrons to move through it easily

Examples : plastic around wires, wood doors, fiberglass, rubbers

Notice what the handles are made of. Why?

“Conductors and insulators” clip

ElectroscopeElectroscope

A device made up of A device made up of two thin metal leaves two thin metal leaves attached to a attached to a knobbed metal rod. knobbed metal rod. The leaves can move The leaves can move and hang straight and hang straight down when not down when not charged. This device charged. This device is used to detect is used to detect electric charges.electric charges.

LightningLarge static discharge

Air masses move and swirl

Top +Bottom -

Negative charge induces a + chargeon ground (repel e-)

Bottom accumulates enough -

Electrons in cloud attractedto ground

When electrons get close to ground

Positive charges are attracted

Connection made

= lightning

Electric charges move through air collide with atoms/molecules

Collisions cause atoms/molecules to emit light

Powerful sound waves

Electrons are ripped off atoms in the airProduce great amounts of heat

Warms surrounding air to 25,000 C (2.5x hotter than Sun surface)

Heat causes air in path to expand rapidly sound waves = Thunder

Earth is a large neutral object

Connection (conductor) will transfer any excess electric charge

“Grounding” – the act of making a connection for an electric charge to

go to the Earth(Lightning rods)

“Lightning” clip

“Van de Graff” clip with safety from static discharge

Video quiz static electricity

ResistanceResistance RESISTANCE is the RESISTANCE is the

tendency for a material tendency for a material to oppose the flow of to oppose the flow of electrons.electrons.

Causes the Causes the ELECTRICALELECTRICAL energy energy to change into to change into THERMALTHERMAL energy and energy and LIGHTLIGHT..

Filament in light-bulb Filament in light-bulb has high resistance so has high resistance so it heats up and glowsit heats up and glows

The amount of resistance is different for The amount of resistance is different for each type of conductor.each type of conductor.

Resistance is measured in ohms. Its symbol Resistance is measured in ohms. Its symbol

is is ΩΩ.. This is the Greek letter omega This is the Greek letter omega

Resistance in wiresResistance in wires

Resistance is caused by electrons running Resistance is caused by electrons running into each other or the walls of the wire.into each other or the walls of the wire.

Resistance is caused by friction which Resistance is caused by friction which means heat will be present.means heat will be present.

Longer, thin wires have MORE resistance than short, thick wires

The resistance of a material will increase (The resistance of a material will increase (↑↑) )

as the temperature increases as the temperature increases ((↑↑) in most ) in most conductors. conductors.

This is why electrical equipment does not This is why electrical equipment does not work as well if it has been on for an extended work as well if it has been on for an extended time.time.

Electric CurrentElectric Current

Similar to Similar to HEATHEAT which flows from areas of which flows from areas of high temps to areas of low temps, high temps to areas of low temps, ELECTRONS flow from places of high ELECTRONS flow from places of high potential energy to places of lower PE.potential energy to places of lower PE.

A negatively charged object has more PE A negatively charged object has more PE than an uncharged onethan an uncharged one

When electrons do get to move (like in a When electrons do get to move (like in a spark of static discharge) the potentials spark of static discharge) the potentials become equal and the flow stops.become equal and the flow stops.

Comparison of GPE to potential Comparison of GPE to potential differencedifference

1.5 V

0.0 V

To Lower Energy

Potential DifferencePotential Difference

1.5 Meters

The potential difference (voltage) is 1.5 V.

Potential Energy (height)

Electrical EnergyElectrical Energy - - Moving electrons in a path is Moving electrons in a path is

electricityelectricity Electrical Potential Difference (v) is measured in Volts Electrical Potential Difference (v) is measured in Volts The rate of moving electric charges, Electric Current (I), is measured in The rate of moving electric charges, Electric Current (I), is measured in

Amperes Amperes Resistance or opposition to the movement of the energy is called Resistance Resistance or opposition to the movement of the energy is called Resistance

(R). (R). I = I = VV R R

Circuits – 2 types Circuits – 2 types

Series circuits are Series circuits are the most simple. the most simple.

One COMPLETE (1) One COMPLETE (1) path for the current path for the current to travel. to travel.

Contains an energy Contains an energy source, a path, and a source, a path, and a load (something for it load (something for it to do, like a lamp) to do, like a lamp)

Circuits – 2 typesCircuits – 2 types Parallel circuits Parallel circuits

provide more provide more than one path for than one path for the current to the current to travel. travel.

Most circuits are Most circuits are parallel, since if parallel, since if one lamp goes one lamp goes out, the others out, the others can stay lit. can stay lit.

F. QG. RH. SJ. T

Which switches, if opened, will cause the light bulb to stop

glowing?

It is the only switch in series to both the battery and light.

USE THE FORMULA SHEET!!USE THE FORMULA SHEET!!

What is the current in a copper wire that What is the current in a copper wire that has a resistance of 2 ohms and is has a resistance of 2 ohms and is connected to a 9 volt electrical source?connected to a 9 volt electrical source?

A. 0.22 ampA. 0.22 amp

B. 4.5 ampsB. 4.5 amps

C. 11.0 ampsC. 11.0 amps

D. 18.0 ampsD. 18.0 amps

V = I R so,

9V = I x 2 ohms or 4.5 amps

ElectrocutionElectrocution

Historical perspective on ElectricityHistorical perspective on Electricity

600 B.C.600 B.C. Thales of Thales of MiletusMiletus writes that the writes that the Greeks had discovered Greeks had discovered that rubbing fur on certain that rubbing fur on certain substances such as substances such as amberamber would cause an would cause an attraction between the attraction between the two. The amber would two. The amber would attract light things such as attract light things such as hair and if rubbed long hair and if rubbed long enough produced a spark.enough produced a spark.

250 B.C.250 B.C. Baghdad BatteryBaghdad Battery– Object found in Iraq in Object found in Iraq in

1938 (and1938 (and dated back dated back to 250 BC) to 250 BC) resembles resembles a galvanic cell and is a galvanic cell and is thought to have been thought to have been used for electroplatingused for electroplating

– Electroplating is the Electroplating is the use of electricity to use of electricity to cover something with cover something with certain metalscertain metals

1550 A.D.1550 A.D. Italian physician Girolamo Cardano in his Italian physician Girolamo Cardano in his De De

SubtilitateSubtilitate distinguishes difference between distinguishes difference between electrical and magnetic forceselectrical and magnetic forces

1600 A.D.1600 A.D. English scientist English scientist

William Gilbert writes William Gilbert writes De MagnateDe Magnate coined coined the Latin word the Latin word electricuselectricus from the from the Greek word Greek word ηλεκτρονηλεκτρον ((elektronelektron), ),

Ηλεκτρον Ηλεκτρον means means “amber” in Greek“amber” in Greek

English words electric English words electric and electricity came and electricity came fromfrom

1660 A.D. Otto von 1660 A.D. Otto von Guericke invents an Guericke invents an electrostatic generatorelectrostatic generator

1675 A.D. Robert Boyle determines that electric forces can attract or repel through a vacuum

1729 A.D. Stephen Gray classifies materials as either conductors or insulators

1729 A.D. C.F. Du Fay identifies positive and negative charges

1752 A.D.1752 A.D. Benjamin Franklin legend says that Benjamin Franklin legend says that

he conducted famous, yet extremely he conducted famous, yet extremely dangerous experiment of flying kite dangerous experiment of flying kite with metal key attached during with metal key attached during lightning storm linking lightning with lightning storm linking lightning with electricity.electricity.

He saw that the fibers on the string were standing up and also received a shock from the key when he touched it.

Franklin Franklin invented the invented the lightning rod to lightning rod to protect protect structures by structures by directing the directing the charge to the charge to the ground.ground.

•Georg Wilhelm Richmann of St. Petersburg, Russia died performing kite experiment in 1753

Michael Faraday

Thomas Edison

Nikola Tesla