Charging By FrictionCharging By Friction

When two objects are When two objects are rubbedrubbed together, the together, the molecules are close enough together that molecules are close enough together that

the electrons from one substance can the electrons from one substance can move onto the other substance.move onto the other substance.

The substance that The substance that gains extra electronsgains extra electrons becomes negatively charged, while the becomes negatively charged, while the substance with fewer electrons becomes substance with fewer electrons becomes positivelypositively charged. charged.

The more rubbing, the more transfer, the The more rubbing, the more transfer, the greatergreater the charge. the charge.

The Electrostatic SeriesThe Electrostatic Series

As previously discussed, some objects As previously discussed, some objects hold their electrons tighter than others.hold their electrons tighter than others.

The electrostatic series ranks objects by The electrostatic series ranks objects by how easily they let go of e-how easily they let go of e- during during friction.friction.

Substances that let go easily are on Substances that let go easily are on toptop and become positively charged.and become positively charged.

Substances on the Substances on the bottombottom hold tight and hold tight and take on a negative charge. take on a negative charge.

The further the substances are apart, the The further the substances are apart, the more charge that it produced.more charge that it produced.

++AcetateAcetateGlassGlassWoolWool

Fur or hairFur or hairSilkSilk

AluminiumAluminiumCottonCotton

Paraffin waxParaffin waxPlasticPlasticRubberRubber

GoldGold--

ExampleExample

When clothes are put in a dryer without When clothes are put in a dryer without fabric softener, they rub against each fabric softener, they rub against each other and become charged.other and become charged.

Which item would take on which charge if:Which item would take on which charge if:

a)a) Cotton socks are dried with a wool sweater?Cotton socks are dried with a wool sweater?

-- + +

b) A wool sock is dried with a silk shirt?b) A wool sock is dried with a silk shirt?

++ --

When you comb your hair with a plastic When you comb your hair with a plastic comb, your hair becomes statically comb, your hair becomes statically charged. charged.

What is the charge on your hair?What is the charge on your hair?

++

On the comb?On the comb?

--

What could you use to make a comb that What could you use to make a comb that would produce less charge?would produce less charge?

Hair +Hair + AluminiumAluminium

Comb -Comb - AcetateAcetate

Charging By ContactCharging By Contact

Electric charge can be transferred Electric charge can be transferred between objects just by between objects just by touching them touching them togethertogether..

Charging by conduction occurs when a Charging by conduction occurs when a chargedcharged object touches a object touches a neutralneutral object. object.

A few electrons move from one object to A few electrons move from one object to the other (electrons try to move where the other (electrons try to move where they are needed).they are needed).

As a result, both objects end up with the As a result, both objects end up with the samesame charge. charge.

Charging By IntroductionCharging By Introduction

Neutral objects are attracted to charged Neutral objects are attracted to charged objects. objects.

In fact, a charged object can In fact, a charged object can induceinduce a a charge in another object.charge in another object.

The neutral object never actually The neutral object never actually gainsgains or or losesloses any electrons. any electrons.

When the charged object is brought close, When the charged object is brought close, the electrons the electrons move slightlymove slightly in the in the uncharged object.uncharged object.

So if a positive object in brought near, the So if a positive object in brought near, the electrons are electrons are aattractedttracted and move and move closercloser..

If the charge is negative, the electrons are If the charge is negative, the electrons are repelledrepelled and move and move awayaway..

Discharging An ObjectDischarging An Object

If you connect an electrical device or If you connect an electrical device or something with a charge to the something with a charge to the earthearth or or the the groundground, then the extra charges get , then the extra charges get transferred into the Earth.transferred into the Earth.

Since the Earth is so large, it can accept a Since the Earth is so large, it can accept a lot of electrons without having much effect.lot of electrons without having much effect.

This is called This is called groundinggrounding an object. an object.