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發表於 13-9-2008 19:34:42
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少到可以當無.
會考生可以假設insulator是沒有free electrons,完完全全跟conductor劃清界線就可以.
insulator第2個名叫dielectric material,在AC電下,同埋符合某些條件,就會polarize,間接通電. Capacitor既原理好類似,不過佢係用electrolyte做polarization,所以唔駛太高壓就成事....而如果想佢直接黎,好似conductor咁呢,就要好高壓先得..此時就會dielectric breakdown,變成ions.....其實係破壞左佢...
proton唔會郁,只有electron會郁,但係electron走左就會留低個hole,movement of hole is opposite to that of electrons, 所以我地當holes係+ve charge. yr1既電子野,已經忘記得7788.....
關於insulator的conductivity,自己睇.
Physics of conduction in solids
Electrical insulation is the olamba of electrical conduction. Electronic band theory (a branch of physics) predicts that a charge will flow whenever there are states available into which the electrons in a material can be excited. This allows them to gain energy and thereby move through the conductor (usually a metal). If no such states are available, the material is an insulator.
Most (though not all, see Mott insulator) insulators are characterized by having a large band gap. This occurs because the "valence" band containing the highest energy electrons is full, and a large energy gap separates this band from the next band above it. There is always some voltage (called the breakdown voltage) that will give the electrons enough energy to be excited into this band. Once this voltage is exceeded, the material ceases being an insulator, and charge will begin to pass through it. However, it is usually accompanied by physical or chemical changes that permanently degrade the material's insulating properties.
Materials that lack electron conduction must also lack other mobile charges as well. For example, if a liquid or gas contains ions, then the ions can be made to flow as an electric current, and the material is a conductor. Electrolytes and plasmas contain ions and will act as conductors whether or not electron flow is involved.
[ 本帖最後由 [S]【YU】 於 13-9-2008 19:42 編輯 ] |
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