Make careful observations and Make careful observations and record them on your whiteboards.record them on your whiteboards.

Take a few minutes to talk to your Take a few minutes to talk to your neighbors. What is going on? What is neighbors. What is going on? What is causing the meter stick to rotate? Is causing the meter stick to rotate? Is there a force acting? Explain.there a force acting? Explain.

What do you think?What do you think?

ElectrostaticsElectrostatics

ElectrostaticsElectrostatics

Electrostatics involves Electrostatics involves electric electric chargescharges , the forces between them, , the forces between them, and their behavior in materials.and their behavior in materials.

Electric Charges and Electric Charges and ForcesForces

There are two types of charge: There are two types of charge:

positivepositive charges and charges and negativenegative charges charges

ATTRACTREPEL REPEL

Like charges repel, opposite charges attract.

Electrons, Protons, & Electrons, Protons, & AtomsAtoms

Helium atom

Electrons

Protons

Atoms are made up of small particles Atoms are made up of small particles called protons, neutrons, and called protons, neutrons, and electrons.electrons.

ElectronsElectrons carry negative (-) charge. carry negative (-) charge. Loosely bound to atoms and Loosely bound to atoms and

therefore easily transferred from therefore easily transferred from one atom to another.one atom to another.

ProtonsProtons carry positive (+) charge. carry positive (+) charge. Tightly locked within the nucleus Tightly locked within the nucleus

and therefore not transferred.and therefore not transferred. In an atom, the # of protons = # of In an atom, the # of protons = # of

electrons (i.e. neutral—no net electrons (i.e. neutral—no net charge).charge).

Objects are usually neutral but can Objects are usually neutral but can easily acquire or lose electrons to easily acquire or lose electrons to become charged.become charged.

Conductors and Conductors and InsulatorsInsulators Q: What is meant by the Q: What is meant by the

term term electrical electrical conductorconductor?? Provide a few examples.Provide a few examples.

Q: What is meant by the Q: What is meant by the term term electrical insulatorelectrical insulator?? Provide a few examples.Provide a few examples.

Q: Why do conductors Q: Why do conductors and insulators behave and insulators behave differently?differently?

A: Conductors allow A: Conductors allow electrons to flow freely electrons to flow freely through them.through them. Silver, copper, aluminum, Silver, copper, aluminum,

and other metalsand other metals

A: Electrons do not flow A: Electrons do not flow freely though insulators.freely though insulators. Plastic, rubber, glassPlastic, rubber, glass

A: Outer electrons in A: Outer electrons in metals are loosely bound metals are loosely bound to the nucleus and to the nucleus and relatively free to move.relatively free to move.

Charging by ContactCharging by Contact

Electrons move easily so an Electrons move easily so an object can become charged object can become charged by rubbing electrons off the by rubbing electrons off the object’s surface.object’s surface. Ex) Brushing your hair with a Ex) Brushing your hair with a

plastic comb.plastic comb. Walk across a carpet with Walk across a carpet with

plastic-soled shoes.plastic-soled shoes. When rubbing a balloon on When rubbing a balloon on

your hair, electrons are your hair, electrons are attracted to the balloon and attracted to the balloon and transfer.transfer. The balloon is left with excess The balloon is left with excess

electrons (- charge).electrons (- charge). The hair is left with an equal The hair is left with an equal

excess of protons (+ charge).excess of protons (+ charge).

Electrons taken off of fur onto rubber rod

Charging by Contact Charging by Contact (Conductors)(Conductors)

When charging metal, the charge may When charging metal, the charge may move through your body into the move through your body into the ground.ground. The metal and your body are conductors, so The metal and your body are conductors, so

the charge moves through them.the charge moves through them. You must hold the conductor with an You must hold the conductor with an

insulating material, such as rubber gloves, insulating material, such as rubber gloves, to keep the charge on the metal.to keep the charge on the metal.

DemoDemo: Electroscope: Electroscope

The “legs” of an The “legs” of an electroscope electroscope separate when separate when the the electroscope is electroscope is charged due to charged due to the repulsion of the repulsion of like charge on like charge on the two legs.the two legs.

Charged plastic rod deposits negative charge (electrons) onto electroscope.

“Legs”

DemoDemo: Van de Graff : Van de Graff GeneratorGenerator

The Human ElectroscopeThe Human Electroscope Van de Graff deposits Van de Graff deposits

large quantities of large quantities of excess charge on its excess charge on its globe.globe.

A person with long A person with long hair can become a hair can become a human electroscope. human electroscope.

Conservation of ChargeConservation of Charge

+++ ++

Rod & FurNeutral

Electrons are rubbed off the Electrons are rubbed off the hairs of a piece of fur, hairs of a piece of fur, collecting and charging a collecting and charging a plastic rod.plastic rod. Is the fur also charged?Is the fur also charged? Positive or negative.Positive or negative.

Charge cannot be created nor destroyed.Objects become charged by transfer of charges.

Charging by InductionCharging by Induction A charged rod is held A charged rod is held

near a metal sphere. near a metal sphere. Why do the charges in Why do the charges in the metal arrange the metal arrange themselves as shown?themselves as shown?

The metal sphere is The metal sphere is connected to the connected to the ground with a ground with a conductor. Why did conductor. Why did some of the electrons some of the electrons move off the sphere?move off the sphere?

Charging by InductionCharging by Induction The conductor The conductor

connecting the sphere connecting the sphere to ground is removed. to ground is removed. What type of net What type of net charge does the charge does the sphere now possess?sphere now possess?

The negatively The negatively charged rod is charged rod is removed. Why do the removed. Why do the charges move into the charges move into the positions shown?positions shown?

Demo: Charging by Demo: Charging by InductionInduction

Can separate charges by inducing them to Can separate charges by inducing them to opposite sides of a conducting object.opposite sides of a conducting object.

StartNeutral

Induce +’sto one side

Allow –’sto Escape

Finish withnet + charge

DemoDemo: Electroscope & : Electroscope & InductionInduction

The legs of the The legs of the electroscope electroscope separate when separate when charged rod charged rod brought brought nearnear the the electroscope.electroscope.

Charge induction Charge induction pushes electrons pushes electrons into the legs.into the legs.

Negatively charged rod repels electrons so they move as far away as possible.

“Legs”

++++

++

Surface ChargesSurface Charges Why does a charged balloon Why does a charged balloon

stick to the wall?stick to the wall? A positive surface charge is A positive surface charge is

induced on the wall by the induced on the wall by the negatively-charged balloon.negatively-charged balloon. Electrons shift within atoms Electrons shift within atoms

due to attraction or repulsion.due to attraction or repulsion. The insulator does not have a The insulator does not have a

net charge. net charge. The diagram shows the The diagram shows the

opposite case.opposite case. Why can a charged comb Why can a charged comb

pick up little pieces of paper?pick up little pieces of paper?

DemoDemo: Static “Cling”: Static “Cling”

Charged object attracts a neutral insulator by Charged object attracts a neutral insulator by inducing charge polarization in the neutral object. inducing charge polarization in the neutral object.

ChargedBalloon

NeutralWall

Po

lari

zatio

n

Polarization

ChargedComb

NeutralPaper

CCheck Yourselfheck Yourself

What causes a What causes a stream of water to stream of water to be deflected when be deflected when you bring a you bring a charged object charged object next to it?next to it?

Lightning StormsLightning Storms

Charge separates inside Charge separates inside of thunderclouds.of thunderclouds.

The lower part of the The lower part of the cloud is negatively cloud is negatively charged.charged.

This induces a positive This induces a positive charge on the ground.charge on the ground.

When the voltage When the voltage difference is high difference is high enough, a lightning enough, a lightning bolt can occur.bolt can occur.

Make careful observations and record Make careful observations and record them on your whiteboards.them on your whiteboards.

Take a few minutes to talk to your Take a few minutes to talk to your neighbors. What is going on? What is neighbors. What is going on? What is causing the meter stick to rotate? Is causing the meter stick to rotate? Is there a force acting? Is the meter stick there a force acting? Is the meter stick a conductor or an insulator? Explain.a conductor or an insulator? Explain.

What do you think?What do you think?