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.
原帖由 [S]【YU】 於 13-9-2008 19:34 發表
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 ...
原帖由 [S]【YU】 於 13-9-2008 19:34 發表
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 ...
原帖由 [S]【YU】 於 13-9-2008 19:34 發表
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 ...
原帖由 adamsteve 於 16-9-2008 17:24 發表
係喎 佢講緊insulator喎 我停左係哥堆野度喎
1614 c+算係咁架啦 仲要淨係溫高佬哥part 哈哈
但係insulator 夠voltage都係可以breakdown佢架啦 無可能錯ge
唔夠啦爆唔開佢 爆唔開咪傳唔到電lo
原帖由 Zend 於 22-9-2008 20:15 發表
Financial Meltdown/Tsunami 對於science field in HK 都係一樣gum _ _ [[tk_02]]
原帖由 [S]【YU】 於 23-9-2008 17:37 發表
derivatives既存在,本是一件好事.
但不正當咁使用,就會變成自殺既工具.
hku 既朋友,如對derivative有興趣,可考慮take fina1001 / fina1003 ,然後再讀 fina0301.
此兩courses應該都係open to all students 的 BB ...
原帖由 [S]【YU】 於 22-9-2008 21:44 發表
[[tk_26]] 喵喵怪金句:「就係咁嘞!」
看來adamsteve還沒有忘記PC Chui 哄人入局的一番說話.
係問題愈黎愈多既現今社會,科技係永遠都唔會被忽視.
原帖由 piyopiyo 於 24-9-2008 07:23 AM 發表
3個HKU 人係度訴苦[[tk_43]]
你地有無探望過入左dental ge Albie同AC ge HKwww[[tk_09]]
原帖由 Zend 於 25-9-2008 00:11 發表
dental ...-.-
好似好遠
AC ,理論上讀Stat 係會有機會見到
可惜我完全係chem/biochem 佬~~ so byebye
原帖由 adamsteve 於 27-9-2008 15:27 發表
有人開門CU人都可以跟住入黎架
成個CAMPUS 9成地方都係OPEN TO PULBIC
今個禮拜打左一日風咋MA 咪禮拜二LO
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