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مقدمه ای بر الکتریسیته بخش دوم

» نوع مطلب : آموزش‌ ،

Conductors and Insulators

Elements of an Atom.             

 All.matter.is.made.up.atoms..Atoms.have.a.nucleus.with. electrons.in.motion.around.it..The.nucleus.is.composed.of. protons.and.neutrons.(not.shown)..Electrons.have.a.negative. charge.(-)..Protons.have.a.positive.charge.(+)..Neutrons.are. neutral..In.the.normal.state.of.an.atom,.the.number.of.electrons. is.equal.to.the.number.of.protons.and.the.negative.charge.of. the.electrons.is.balanced.by.the.positive.charge.of.the.protons

Free Electrons.                    

Electrons.move.about.the.nucleus.at.different.distances..The. closer.to.the.nucleus,.the.more.tightly.bound.the.electrons.are. to.the.atom..Electrons.in.the.outer.band.can.be.easily.force.out. of.the.atom.by.the.application.of.some.external.force.such.as.a. magnetic.field,.friction,.or.chemical.action.

Electrons.forced.from.atoms.are.sometimes.called.free electrons..A.free.electron.leaves.a.void.which.can.be.filled.by.

an.electron.forced.out.of.another.atom.

 

  Conductors.

 

An.electric current.is.produced.when.free.electrons.move.

from.atom.to.atom.in.a.material..Materials.that.permit.many. electrons.to.move.freely.are.called.conductors..Copper,.silver,. gold,.aluminum,.zinc,.brass,.and.iron.are.considered.good. conductors..Of.these.materials,.copper.and.aluminum.are.the. ones.most.commonly.used.as.conductors..

 

 

 

Insulators.

 

Materials.that.allow.few.free.electrons.are.called.insulators.. Materials.such.as.plastic,.rubber,.glass,.mica,.and.ceramic.are. good.insulators.

An.electric.cable.is.one.example.of.how.conductors.and. insulators.are.used..Electrons.flow.along.a.copper.or.aluminum. conductor.to.provide.energy.to.an.electric.device.such.as.a. radio,.lamp,.or.a.motor..An.insulator.around.the.outside.of. the.copper.conductor.is.provided.to.keep.electrons.in.the. conductor.

 

 

Semiconductors.

 

Semiconductor.materials,.such.as.silicon,.can.be.used.

to.manufacture.devices.that.have.characteristics.of.both. conductors.and.insulators..Many.semiconductor.devices.act.like. a.conductor.when.an.external.force.is.applied.in.one.direction. and.like.an.insulator.when.the.external.force.is.applied.in.the. opposite.direction..This.principle.is.the.basis.for.transistors,. diodes,.and.other.solid-state.electronic.devices..

 

Transistor

 

 Diode

 

 

Review 1

 

1..    List.the.three.basic.particles.of.an.atom.and.state.the. charge.of.each.(positive,.negative,.or.neutral)..

.

.       Element..           Charge

.

.  .           .

.

.

                .

               

 

.

 

                .

 

               

 

.

 

                .

 

               

 

2..    Materials.that.permit.many.electrons.to.move.freely.are. called.    .

 

3..    Which.of.the.following.materials.are.good.conductors?

 

.

a..copper.

.

e..

aluminum

.

b..plastic..

.

f..

glass

.

c..silver. .

.

g..

iron

.

d..rubber.

.

h..

mica

 

4..    Materials.that.allow.few.free.electrons.are.called

.                      .

 

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نوشته شده در : جمعه 17 آذر 1391  توسط : جواد خانی.    نظرات() .

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