Static ElectricityStatic Electricity

Water and Static Water and Static ElectricityElectricity

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What is Electricity?What is Electricity?Historical IdeasHistorical Ideas

The ancient Greeks knew about static The ancient Greeks knew about static electricity and the existence of 2 electricity and the existence of 2 types of charge.types of charge.

In the 1700’s there was an emerging In the 1700’s there was an emerging idea that some items were “electrics” idea that some items were “electrics” (they attracted objects when rubbed) (they attracted objects when rubbed) and others were “non-electrics” (did and others were “non-electrics” (did not attract objects when rubbed)not attract objects when rubbed) No one could explain why!No one could explain why!

““Charge” is the name we apply to the Charge” is the name we apply to the property, and objects can be charged by property, and objects can be charged by frictionfriction

Charge gives rise to forces of attraction Charge gives rise to forces of attraction and repulsionand repulsion

Observing attraction and repulsion, we Observing attraction and repulsion, we can say that two charge states existcan say that two charge states exist

Opposites AttractOpposites Attract

Charges that are Charges that are like (that is, like (that is, created in similar created in similar circumstances) circumstances) repelrepel

Charges which Charges which are unlike (that is, are unlike (that is, created in created in different different circumstances) circumstances) attractattract

A neutral object is attracted to A neutral object is attracted to both positive and negative chargesboth positive and negative charges

Charles du Fay (1698 – Charles du Fay (1698 – 1739)1739)

A French physicistA French physicist Began his Began his

experiments in the experiments in the 1700’s1700’s

Discovered that a Discovered that a cork ball touched by cork ball touched by an “electrified” glass an “electrified” glass rod would attract rod would attract another cork ball another cork ball touched by an touched by an “electrified” resin rod.“electrified” resin rod.

Two Fluid TheoryTwo Fluid Theory

His results led du Fay to conclude His results led du Fay to conclude that there were two kinds of electric that there were two kinds of electric “fluids”“fluids” 1. Vitreous Electricity 1. Vitreous Electricity 2. Resinous Electricity2. Resinous Electricity

The Two Fluid Theory The Two Fluid Theory Says Says

1. All objects contain both fluids1. All objects contain both fluids 2. An “electrically neutral” object has 2. An “electrically neutral” object has

equal amountequal amounts of vitreous and resinous s of vitreous and resinous fluids.fluids.

3. An object is vitreous if it has more 3. An object is vitreous if it has more vitreous fluid and resinous if it has more vitreous fluid and resinous if it has more resinous fluidresinous fluid

4. When two objects come into contact 4. When two objects come into contact with each other the fluids transfer from with each other the fluids transfer from one object to another to balance out and one object to another to balance out and become electrically neutral.become electrically neutral.

The ProblemThe Problem

What happens when two vitreous What happens when two vitreous objects touch?objects touch?

What happens when two resinous What happens when two resinous objects touch?objects touch?

Why do objects attract and repel Why do objects attract and repel each other? Shouldn’t everything each other? Shouldn’t everything attract everything else if everything attract everything else if everything contains both fluids?contains both fluids?

Benjamin FranklinBenjamin Franklin

Began studying Began studying electricity in 1752.electricity in 1752.

Rejected du Fay’s Rejected du Fay’s two fluid theory.two fluid theory.

Franklin was the Franklin was the first to use the first to use the terms terms positive positive and and negative negative to to describe describe electricity.electricity.

One Fluid TheoryOne Fluid Theory

Franklin proposed that there is only Franklin proposed that there is only one electrical fluid and an object is one electrical fluid and an object is positively or negatively “charged” positively or negatively “charged” depending on how much fluid it has.depending on how much fluid it has. A “neutral” object has just enough fluidA “neutral” object has just enough fluid A “positive” object has too much fluidA “positive” object has too much fluid A “negative” object has too little fluidA “negative” object has too little fluid

How the one fluid theory How the one fluid theory solves the problems of the solves the problems of the

two fluid theorytwo fluid theory Positive and negative objects attract each Positive and negative objects attract each

other because the extra fluid from the other because the extra fluid from the positive object flows into the negative positive object flows into the negative objectobject

Like charges repel because:Like charges repel because: 1. A positive charged object won’t take the 1. A positive charged object won’t take the

extra electrical fluid from another positive extra electrical fluid from another positive objectobject

2. A negative charged object doesn’t have 2. A negative charged object doesn’t have extra fluid to give to another negative charged extra fluid to give to another negative charged objectobject

A Modern Look A Modern Look at Electricityat Electricity

The Modern Atomic TheoryThe Modern Atomic Theory( A review of Atoms and ( A review of Atoms and

Elements)Elements) 1. Atoms are made up of positive 1. Atoms are made up of positive

particles called particles called protonsprotons, negative , negative particles called particles called electrons electrons and neutral and neutral particles called particles called neutronsneutrons..

2. Protons and neutrons are found in 2. Protons and neutrons are found in the nucleus of the atom while the nucleus of the atom while electrons orbit around the nucleuselectrons orbit around the nucleus

3. Atoms are electrically neutral so:3. Atoms are electrically neutral so: The # of protons = The # of electronsThe # of protons = The # of electrons

The Particle Model of The Particle Model of Electric ChargeElectric Charge

Developed from 20Developed from 20thth century century experimentation. This is the model experimentation. This is the model currently accepted as correct.currently accepted as correct.

This theory states that This theory states that charge is a charge is a result of the presence of protons result of the presence of protons and electrons.and electrons.

The 3 Electrical StatesThe 3 Electrical States

According to the particle model of According to the particle model of electric charge, an object can exist electric charge, an object can exist in 3 electrical states.in 3 electrical states. 1. An object can be Neutral1. An object can be Neutral

# of protons = # of electrons# of protons = # of electrons 2. An object can be Positive2. An object can be Positive

more protons than electronsmore protons than electrons 3. An object can be Negative3. An object can be Negative

More electrons than protonsMore electrons than protons

Neutrons are found in the nucleus Neutrons are found in the nucleus where they are fixed and where they are fixed and cannot cannot movemove

Since protons (+) are found in the Since protons (+) are found in the nucleus they are fixed and nucleus they are fixed and cannot cannot move.move.

Electrons (-) are moving around the Electrons (-) are moving around the nucleus and as a result are nucleus and as a result are free to free to move.move.

Neutral AttractionNeutral Attraction

Bring a positively charged rod near bits of Bring a positively charged rod near bits of paper, and the paper will be attracted to the paper, and the paper will be attracted to the rodrod

However, the paper is However, the paper is notnot negatively negatively charged!charged! How do we know? If the paper was negatively How do we know? If the paper was negatively

charged, then the bits of paper would be charged, then the bits of paper would be repelling each otherrepelling each other

Bring a negatively charged rod near the Bring a negatively charged rod near the paper, and the paper will be attracted to the paper, and the paper will be attracted to the rodrod

ConductorsConductors

Substances that allow electrical Substances that allow electrical charge to pass through them easily.charge to pass through them easily.

Conductors have electrons that are Conductors have electrons that are not tightly held by their nuclei which not tightly held by their nuclei which allows electrons to move easily. allows electrons to move easily. Electrons are able to “flow”Electrons are able to “flow”

ExamplesExamples MetalsMetals Ions in waterIons in water The human bodyThe human body

InsulatorsInsulators

Substances that do not allow electric Substances that do not allow electric charge to pass through them easily.charge to pass through them easily.

Insulators have electrons that are Insulators have electrons that are more strongly attached to their more strongly attached to their nuclei.nuclei.

ExamplesExamples GlassGlass PlasticsPlastics WaterWater AirAir

Charging by FrictionCharging by Friction

An object can be charged by rubbing An object can be charged by rubbing it (friction) because this action can it (friction) because this action can cause the electrons to be pulled off cause the electrons to be pulled off of or deposited onto the objectof or deposited onto the object

The electrons are unable to flow and The electrons are unable to flow and therefore the transferred electrons therefore the transferred electrons will stay where they are placed.will stay where they are placed.

Electron AffinityElectron Affinity

The transfer of electrons is The transfer of electrons is determined by the determined by the Electron AffinityElectron Affinity of the object.of the object. When 2 objects are rubbed together, When 2 objects are rubbed together,

the object with the highest Electron the object with the highest Electron Affinity will take electrons from the Affinity will take electrons from the other object becoming negative.other object becoming negative.

The object that loses electrons becomes The object that loses electrons becomes positive.positive.

Answer these Questions in Answer these Questions in your Notes: Electrostatic your Notes: Electrostatic

PhenomenaPhenomena 1. Why is a glass rod positively 1. Why is a glass rod positively

charged when it is rubbed with silk?charged when it is rubbed with silk?

2.Why is a glass rod negatively 2.Why is a glass rod negatively charged when rubbed with wool?charged when rubbed with wool?

Charge is not created or destroyed, Charge is not created or destroyed, but rather moved aroundbut rather moved around

Diagram (p. 3.9)Diagram (p. 3.9)

Charging Objects by Charging Objects by ConductionConduction

A neutral object can be “charged” by A neutral object can be “charged” by coming in coming in contactcontact with a charged with a charged object.object.

Charge is transferred between the Charge is transferred between the neutral object and the charged neutral object and the charged object.object.

Charging by InductionCharging by Induction

Charging a neutral object Charging a neutral object WITHOUT WITHOUT contactcontact

There are two types of induced There are two types of induced charge;charge; Temporary Induced ChargeTemporary Induced Charge Permanent Induced ChargePermanent Induced Charge

Temporary Induced Temporary Induced ChargeCharge

A (+) charged object A (+) charged object is brought near a is brought near a neutral conductor.neutral conductor.

The (+) charged The (+) charged object attracts the (-) object attracts the (-) charges to the end of charges to the end of the conductor the conductor nearest it.nearest it.

This creates a This creates a Charge SeparationCharge Separation the conductor now the conductor now

has a positive and a has a positive and a negative endnegative end

BUT:BUT:

IF THE (+) CHARGED OBJECT IS IF THE (+) CHARGED OBJECT IS REMOVED, THE CONDUCTOR REMOVED, THE CONDUCTOR BECOMES BECOMES NEUTRAL NEUTRAL AGAINAGAIN

Permanent Induced Permanent Induced ChargeCharge

A (+) charged object is brought near A (+) charged object is brought near a neutral conductor and a charge a neutral conductor and a charge separation is created.separation is created.

Permanent Induced Charge:Permanent Induced Charge:GroundingGrounding

The conductor is touched with a The conductor is touched with a finger, producing a conducting path finger, producing a conducting path between the object and the Earthbetween the object and the Earth

The Earth (Ground)The Earth (Ground)

has a huge reservoir of has a huge reservoir of

charges. It can easily absorbcharges. It can easily absorb

or release these charges toor release these charges to

an object when necessary.an object when necessary.

The finger is removed leaving the The finger is removed leaving the excess electrons in the conductor excess electrons in the conductor attracted to the (+) charged object.attracted to the (+) charged object.

The (+) charged object is removed The (+) charged object is removed allowing the excess (-) charges to allowing the excess (-) charges to distribute evenly. This leaves the distribute evenly. This leaves the object with a permanent (-) charge.object with a permanent (-) charge.

The charge that isThe charge that is

induced is oppositeinduced is opposite

to the charge of the to the charge of the

original object.original object.

Why Does this Work?Why Does this Work?

The charge on the object is unable to The charge on the object is unable to move because it is an insulator.move because it is an insulator.

The charge on the sphere can move The charge on the sphere can move because it is a conductorbecause it is a conductor

The (-) charges are forced to move to The (-) charges are forced to move to one end of the sphere because they one end of the sphere because they are attracted to the (+) charge.are attracted to the (+) charge.

If you touch the sphere with your If you touch the sphere with your finger, you become a “ground” and finger, you become a “ground” and provide a path for the electrons from provide a path for the electrons from the Earth to move towards the the Earth to move towards the positive object.positive object.

When you remove your finger , the When you remove your finger , the pathway is broken and the electrons pathway is broken and the electrons are left on the sphere.are left on the sphere.

Who Did What?Who Did What?

ThomsonThomson Discovered the atomDiscovered the atom

MilikanMilikan Oil drop experimentOil drop experiment

RutherfordRutherford Gold foil experimentGold foil experiment Provided consistency between the Provided consistency between the

atomic model of matter and the particle atomic model of matter and the particle modelmodel

Particle Model of Particle Model of ElectricityElectricity

Two types of charge particles, Two types of charge particles, positive (protons) and negative positive (protons) and negative (electrons), exist(electrons), exist

Charge cannot be created or Charge cannot be created or destroyed – charge is conserveddestroyed – charge is conserved

Positive charges are fixed and Positive charges are fixed and negative charges are free to movenegative charges are free to move

A neutral object has equal numbers of A neutral object has equal numbers of positive and negative chargepositive and negative charge

Particle ModelParticle Model

A negative object has an excess of negative A negative object has an excess of negative chargecharge

A positive object has a deficit of negative A positive object has a deficit of negative chargecharge

Charge is shared by contact. Materials Charge is shared by contact. Materials which allow charge to move easily are which allow charge to move easily are called called conductorsconductors and materials which do and materials which do not allow charge to move easily are called not allow charge to move easily are called insulatorsinsulators

Like charges repel; unlike charges attractLike charges repel; unlike charges attract