ConductorsConductors

Local ChargeLocal Charge When an item is charged the When an item is charged the

charge transfer takes place at charge transfer takes place at the point of contact.the point of contact.

Other areas are unaffected.Other areas are unaffected.

InsulatorInsulator If the charges stay in place the If the charges stay in place the

material is an material is an insulatorinsulator..

A vacuum is a perfect A vacuum is a perfect insulator.insulator.

Materials are never perfect Materials are never perfect insulators.insulators.• Some charge movesSome charge moves

• Example: human skinExample: human skin

ConductorConductor If the charges redistribute the If the charges redistribute the

material is a material is a conductorconductor..

Good conductors allow Good conductors allow charges to move freely.charges to move freely.• Metals: copper, iron, etc.Metals: copper, iron, etc.

Some materials change from Some materials change from conductors to insulators under conductors to insulators under different circumstances.different circumstances.• TemperatureTemperature

• LightLight

IonsIons Atoms are made of protons Atoms are made of protons

and electrons bound together.and electrons bound together.• Generally neutralGenerally neutral

When electrons are added When electrons are added removed the atom becomes an removed the atom becomes an ionion..• Ions are charged atoms.Ions are charged atoms.

Impurities in an insulator can Impurities in an insulator can create ions and form a create ions and form a conductor.conductor.• Salt in waterSalt in water

Lightning BoltLightning Bolt Air is a poor conductor.Air is a poor conductor.

If too much charge builds up If too much charge builds up between the air and the between the air and the ground some air can ionize.ground some air can ionize.

The ionized air can carry The ionized air can carry electricity in the form of electricity in the form of lightning.lightning.

Cornell University Extension photo

InductionInduction

Charge can be induced in another object without Charge can be induced in another object without touching the object.touching the object.

Shape and ChargeShape and Charge Excess charge on a conductor Excess charge on a conductor

will always move to the outer will always move to the outer surface.surface.• Like charges repelLike charges repel

• Charges free to moveCharges free to move

Charges will concentrate at Charges will concentrate at pointed regions on the surface.pointed regions on the surface.

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