閃電與電暈(yun)現象(xiang)

富蘭(lan)克林著名的(de)(de)研(yan)究是利用(yong)風箏揭示這種自然(ran)現象的(de)(de)本質，并據此設計(ji)了(le)世界上第一(yi)根避(bi)雷針。閃電(dian)(dian)時，由于云(yun)層與地面間的(de)(de)高(gao)電(dian)(dian)位(wei)差，導致在(zai)大氣(qi)(qi)中產生電(dian)(dian)火花(hua)，其結果(guo)是高(gao)電(dian)(dian)場(chang)使電(dian)(dian)子(zi)加速到很(hen)高(gao)的(de)(de)速度，以至(zhi)于有更多的(de)(de)自由電(dian)(dian)子(zi)與空(kong)氣(qi)(qi)分子(zi)碰撞，從而激(ji)發電(dian)(dian)子(zi)的(de)(de)雪崩過程，使空(kong)氣(qi)(qi)離子(zi)化并產生很(hen)大的(de)(de)電(dian)(dian)流。

富蘭(lan)克林指出，閃(shan)電(dian)(dian)的(de)(de)根源是(shi)放電(dian)(dian)，源于(yu)(yu)云層(ceng)(ceng)(ceng)內電(dian)(dian)荷的(de)(de)分(fen)離，但(dan)對(dui)于(yu)(yu)導(dao)致云層(ceng)(ceng)(ceng)內電(dian)(dian)荷分(fen)離的(de)(de)原(yuan)因目前尚無定論，需要(yao)進一步(bu)的(de)(de)研究。富蘭(lan)克林如(ru)此解(jie)釋(shi)閃(shan)電(dian)(dian)現(xian)象:地面和云層(ceng)(ceng)(ceng)可(ke)(ke)視(shi)為(wei)兩塊平行板，組成巨大(da)的(de)(de)電(dian)(dian)容(rong)器;如(ru)果(guo)空氣中的(de)(de)電(dian)(dian)場足(zu)夠高(gao)，則電(dian)(dian)子就可(ke)(ke)以獲得足(zu)夠的(de)(de)能量，通過分(fen)子的(de)(de)彼此碰(peng)撞使空氣電(dian)(dian)離，從而在(zai)云層(ceng)(ceng)(ceng)和地面間建(jian)立起導(dao)電(dian)(dian)路(lu)徑由(you)于(yu)(yu)閃(shan)電(dian)(dian)現(xian)象由(you)云層(ceng)(ceng)(ceng)的(de)(de)放電(dian)(dian)引發，因而閃(shan)電(dian)(dian)遵循空氣電(dian)(dian)離建(jian)立的(de)(de)導(dao)電(dian)(dian)路(lu)徑。

電(dian)(dian)暈(Corona）可視為(wei)失效的(de)(de)閃(shan)電(dian)(dian)，即不完全的(de)(de)閃(shan)電(dian)(dian)過程。一般來說，如果在(zai)導線(xian)和導電(dian)(dian)表面之間存在(zai)高電(dian)(dian)壓差，則容易產生電(dian)(dian)暈現象。導線(xian)附近的(de)(de)空氣(qi)將(jiang)被擊穿(chuan)而電(dian)(dian)離（離子(zi)化)，因為(wei)作用于(yu)這種(zhong)區(qu)域的(de)(de)電(dian)(dian)場特(te)別(bie)強(qiang);在(zai)遠離導線(xian)的(de)(de)地方，由于(yu)電(dian)(dian)荷(he)載體不能移動得足夠快，以(yi)至于(yu)空氣(qi)無法電(dian)(dian)離或離子(zi)化。在(zai)靜電(dian)(dian)照相技術及類似的(de)(de)應用領(ling)域，電(dian)(dian)暈可以(yi)用作離子(zi)源。

關于(yu)電(dian)暈一詞(ci)(ci)有(you)許多定(ding)義，韋伯斯特(te)詞(ci)(ci)典將電(dian)暈定(ding)義為高電(dian)壓作(zuo)用(yong)下鄰近導電(dian)體(ti)表(biao)面的微弱電(dian)荷流(liu)動，這種電(dian)荷的流(liu)動源于(yu)電(dian)擊穿導致(zhi)的周(zhou)圍空氣的電(dian)離。顯(xian)然(ran)，這種解釋更容易(yi)令人產生(sheng)與靜電(dian)照(zhao)相充電(dian)過(guo)程的聯想，正(zheng)因為電(dian)荷的流(liu)動，才會使光(guang)導體(ti)表(biao)面建立(li)均(jun)勻(yun)分(fen)布的電(dian)荷層。

英文(wen)的(de)(de)(de)Corona一(yi)詞可能(neng)出(chu)(chu)現在(zai)(zai)許(xu)多不(bu)(bu)同的(de)(de)(de)場合(he)，天(tian)文(wen)學、電(dian)(dian)(dian)(dian)學、建(jian)筑(zhu)、植物(wu)學和解剖學都有使(shi)用Corona這(zhe)一(yi)單(dan)詞的(de)(de)(de)例子(zi)，具體含(han)義(yi)可能(neng)有很(hen)大(da)的(de)(de)(de)差異。對應于(yu)天(tian)文(wen)學上的(de)(de)(de)電(dian)(dian)(dian)(dian)暈(yun)現象(xiang)通(tong)常有兩(liang)(liang)種含(han)義(yi)，其一(yi)指出(chu)(chu)現在(zai)(zai)天(tian)體周圍(wei)、帶(dai)有朦朧(long)顏色(se)和不(bu)(bu)規則(ze)(ze)包絡的(de)(de)(de)光(guang)環(huan)，如圖3–1所示那樣,地面上的(de)(de)(de)人通(tong)過(guo)薄霧或薄薄的(de)(de)(de)云層(ceng)(ceng)可以看見這(zhe)種天(tian)文(wen)現象(xiang)，尤其是(shi)出(chu)(chu)現在(zai)(zai)月亮或太陽周圍(wei)的(de)(de)(de)光(guang)環(huan)。電(dian)(dian)(dian)(dian)暈(yun)的(de)(de)(de)產(chan)生源(yuan)于(yu)光(guang)的(de)(de)(de)衍射(she)，光(guang)線來(lai)自(zi)大(da)氣層(ceng)(ceng)物(wu)質的(de)(de)(de)懸浮狀顆(ke)粒。天(tian)文(wen)學中的(de)(de)(de)Corona有時也(ye)稱(cheng)為Aureole，兩(liang)(liang)者的(de)(de)(de)含(han)義(yi)并無區別。此外，天(tian)文(wen)學意(yi)義(yi)上的(de)(de)(de)電(dian)(dian)(dian)(dian)暈(yun)現象(xiang)也(ye)指太陽色(se)球，即太陽的(de)(de)(de)外層(ceng)(ceng)氣體由于(yu)高度的(de)(de)(de)離子(zi)化(hua)而(er)形成的(de)(de)(de)不(bu)(bu)規則(ze)(ze)包絡，這(zhe)種不(bu)(bu)規則(ze)(ze)的(de)(de)(de)包絡會發出(chu)(chu)亮光(guang)。

電(dian)(dian)(dian)學(xue)上Corona的本義指電(dian)(dian)(dian)暈(yun)放電(dian)(dian)(dian)現象，如果(guo)電(dian)(dian)(dian)極(ji)(ji)處于(yu)高電(dian)(dian)(dian)場(chang)的作用下，且周圍環境條件合適，則該電(dian)(dian)(dian)極(ji)(ji)會發出的微弱的光，形成(cheng)類似于(yu)出現在天體周圍的光暈(yun)效果(guo)。在電(dian)(dian)(dian)極(ji)(ji)發生電(dian)(dian)(dian)暈(yun)現象的同(tong)時，還常常伴隨有從(cong)高電(dian)(dian)(dian)場(chang)電(dian)(dian)(dian)極(ji)(ji)到低(di)電(dian)(dian)(dian)場(chang)電(dian)(dian)(dian)極(ji)(ji)的電(dian)(dian)(dian)子流。

電暈現象的(de)工程意義

電(dian)(dian)(dian)(dian)暈(yun)現(xian)象(xiang)(xiang)指帶(dai)(dai)電(dian)(dian)(dian)(dian)體表面在(zai)(zai)氣(qi)體介質中局部放電(dian)(dian)(dian)(dian)的物(wu)理現(xian)象(xiang)(xiang)，帶(dai)(dai)電(dian)(dian)(dian)(dian)體處于液體介質中時同樣如此(ci)，兩(liang)者局部放電(dian)(dian)(dian)(dian)的原理相(xiang)同。需要帶(dai)(dai)電(dian)(dian)(dian)(dian)體表面在(zai)(zai)空氣(qi)中的放電(dian)(dian)(dian)(dian)效(xiao)應，通常發生在(zai)(zai)不均勻(yun)分布的電(dian)(dian)(dian)(dian)場環(huan)境下電(dian)(dian)(dian)(dian)場強度很高的區域(yu)內，例如高壓導(dao)線的周圍區域(yu)和帶(dai)(dai)電(dian)(dian)(dian)(dian)體尖端的附近區域(yu)。電(dian)(dian)(dian)(dian)學意(yi)義上的電(dian)(dian)(dian)(dian)暈(yun)現(xian)象(xiang)(xiang)具有自(zi)身的特點，歸結為出現(xian)與日暈(yun)相(xiang)似的光層，發出嗤嗤的聲音，產生臭氧(yang)和氧(yang)化(hua)氮等物(wu)質。

對(dui)處在均(jun)勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang)中的(de)(de)(de)物(wu)質，由于所有位置的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)場(chang)強度都是(shi)相同(tong)的(de)(de)(de)，因而對(dui)電(dian)(dian)(dian)(dian)(dian)場(chang)中的(de)(de)(de)物(wu)質施加穩態電(dian)(dian)(dian)(dian)(dian)壓(ya)，例如直流或工頻交流，且(qie)電(dian)(dian)(dian)(dian)(dian)場(chang)中的(de)(de)(de)物(wu)質有可能組(zu)成(cheng)(cheng)(cheng)(cheng)電(dian)(dian)(dian)(dian)(dian)極對(dui)時(shi)，只(zhi)要電(dian)(dian)(dian)(dian)(dian)場(chang)強度達到空氣的(de)(de)(de)擊(ji)穿強度，則電(dian)(dian)(dian)(dian)(dian)極對(dui)組(zu)成(cheng)(cheng)(cheng)(cheng)的(de)(de)(de)氣隙(xi)就(jiu)會被(bei)擊(ji)穿。但問題在于，一(yi)般(ban)場(chang)合很難見到均(jun)勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang)，出現略為(wei)(wei)(wei)不(bu)均(jun)勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang)的(de)(de)(de)機會卻相當多(duo)，比(bi)如球(qiu)(qiu)體(ti)與球(qiu)(qiu)體(ti)形(xing)成(cheng)(cheng)(cheng)(cheng)的(de)(de)(de)間(jian)(jian)隙(xi)，圓(yuan)柱(zhu)體(ti)與圓(yuan)柱(zhu)體(ti)組(zu)成(cheng)(cheng)(cheng)(cheng)的(de)(de)(de)間(jian)(jian)隙(xi)，圓(yuan)柱(zhu)體(ti)與平(ping)板組(zu)成(cheng)(cheng)(cheng)(cheng)的(de)(de)(de)間(jian)(jian)隙(xi)，球(qiu)(qiu)體(ti)和平(ping)板形(xing)成(cheng)(cheng)(cheng)(cheng)的(de)(de)(de)間(jian)(jian)隙(xi)等。以(yi)球(qiu)(qiu)體(ti)與球(qiu)(qiu)體(ti)形(xing)成(cheng)(cheng)(cheng)(cheng)的(de)(de)(de)間(jian)(jian)隙(xi)為(wei)(wei)(wei)例，當間(jian)(jian)隙(xi)距(ju)(ju)離(li)小于1/4球(qiu)(qiu)體(ti)直徑(jing)時(shi)，就(jiu)認為(wei)(wei)(wei)加到兩個球(qiu)(qiu)體(ti)間(jian)(jian)隙(xi)上的(de)(de)(de)穩態電(dian)(dian)(dian)(dian)(dian)壓(ya)產生的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)場(chang)可近似處理(li)為(wei)(wei)(wei)均(jun)勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang);若兩球(qiu)(qiu)間(jian)(jian)隙(xi)距(ju)(ju)離(li)在球(qiu)(qiu)體(ti)直徑(jing)的(de)(de)(de)1/4到1/2之間(jian)(jian)，這種(zhong)情況(kuang)下形(xing)成(cheng)(cheng)(cheng)(cheng)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)場(chang)不(bu)再(zai)能近似處理(li)為(wei)(wei)(wei)均(jun)勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang)了(le)，應認為(wei)(wei)(wei)是(shi)略為(wei)(wei)(wei)不(bu)均(jun)勻(yun)的(de)(de)(de)電(dian)(dian)(dian)(dian)(dian)場(chang)。

不(bu)(bu)均勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang)與均勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang)的(de)(de)主要區(qu)別在(zai)于空氣間隙(xi)內各點的(de)(de)電(dian)(dian)(dian)(dian)(dian)場(chang)強(qiang)度(du)(du)不(bu)(bu)均勻(yun)，例(li)如在(zai)電(dian)(dian)(dian)(dian)(dian)力(li)線(xian)比較集中的(de)(de)電(dian)(dian)(dian)(dian)(dian)極(ji)附近電(dian)(dian)(dian)(dian)(dian)場(chang)強(qiang)度(du)(du)最(zui)大，電(dian)(dian)(dian)(dian)(dian)力(li)線(xian)疏的(de)(de)地方電(dian)(dian)(dian)(dian)(dian)場(chang)強(qiang)度(du)(du)很小，如棒(bang)狀(zhuang)物體與棒(bang)狀(zhuang)物體構成的(de)(de)間隙(xi)屬于對稱的(de)(de)不(bu)(bu)均勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang)，由于在(zai)電(dian)(dian)(dian)(dian)(dian)極(ji)的(de)(de)尖端處電(dian)(dian)(dian)(dian)(dian)力(li)線(xian)最(zui)集中，電(dian)(dian)(dian)(dian)(dian)場(chang)強(qiang)度(du)(du)也(ye)最(zui)大。如果在(zai)這(zhe)種對稱形(xing)式的(de)(de)不(bu)(bu)均勻(yun)電(dian)(dian)(dian)(dian)(dian)場(chang)條件下加上高(gao)(gao)電(dian)(dian)(dian)(dian)(dian)壓，就(jiu)會在(zai)電(dian)(dian)(dian)(dian)(dian)極(ji)附近產生空氣的(de)(de)局部放(fang)電(dian)(dian)(dian)(dian)(dian)，這(zhe)就(jiu)是(shi)電(dian)(dian)(dian)(dian)(dian)暈(yun)現象;電(dian)(dian)(dian)(dian)(dian)壓進一步加高(gao)(gao)時，電(dian)(dian)(dian)(dian)(dian)暈(yun)放(fang)電(dian)(dian)(dian)(dian)(dian)效應將(jiang)更加強(qiang)烈(lie)，致使(shi)間隙(xi)內發生刷狀(zhuang)放(fang)電(dian)(dian)(dian)(dian)(dian)，此后就(jiu)擊穿(chuan)了(電(dian)(dian)(dian)(dian)(dian)弧放(fang)電(dian)(dian)(dian)(dian)(dian))。

對于由棒狀物體和平(ping)板組成的(de)間隙，在(zai)尖(jian)電(dian)(dian)(dian)極附(fu)近(jin)電(dian)(dian)(dian)場強(qiang)度(du)最大，雖然加上高(gao)(gao)(gao)壓后電(dian)(dian)(dian)極附(fu)近(jin)先產生(sheng)電(dian)(dian)(dian)暈放電(dian)(dian)(dian)，但(dan)由于平(ping)板上的(de)電(dian)(dian)(dian)力(li)線很疏，因而不會發生(sheng)電(dian)(dian)(dian)暈現(xian)象(xiang)。當電(dian)(dian)(dian)壓足夠(gou)高(gao)(gao)(gao)時，棒狀物體電(dian)(dian)(dian)極也將產生(sheng)刷狀的(de)火花(hua)放電(dian)(dian)(dian)，最后導致電(dian)(dian)(dian)弧放電(dian)(dian)(dian)并擊(ji)穿(chuan)。電(dian)(dian)(dian)暈現(xian)象(xiang)大多(duo)發生(sheng)在(zai)導體殼(ke)曲率半徑(jing)小的(de)位置，因為這(zhe)些(xie)位置（特別是尖(jian)端）的(de)電(dian)(dian)(dian)荷(he)密度(du)很大。而在(zai)緊鄰帶電(dian)(dian)(dian)表面處(chu)，電(dian)(dian)(dian)場強(qiang)度(du)與電(dian)(dian)(dian)荷(he)密度(du)成正(zheng)比，且由于電(dian)(dian)(dian)場強(qiang)度(du)和電(dian)(dian)(dian)荷(he)密度(du)都可能達到極大的(de)數值(zhi)，故在(zai)導體的(de)尖(jian)端處(chu)場強(qiang)很高(gao)(gao)(gao)。由此可見，當空氣周(zhou)圍的(de)導體電(dian)(dian)(dian)勢升(sheng)高(gao)(gao)(gao)時，這(zhe)些(xie)尖(jian)端之處(chu)具備產生(sheng)電(dian)(dian)(dian)暈現(xian)象(xiang)的(de)條件。

空(kong)氣(qi)一般被(bei)視為絕(jue)緣體(ti)(ti)，但空(kong)氣(qi)中(zhong)含(han)有(you)少數由宇宙線照射而產(chan)生的(de)(de)離(li)子(zi)，帶(dai)正電(dian)(dian)的(de)(de)導(dao)(dao)體(ti)(ti)會吸引周圍(wei)空(kong)氣(qi)中(zhong)的(de)(de)負(fu)離(li)子(zi)而自(zi)行慢慢地中(zhong)和(he)。若帶(dai)電(dian)(dian)導(dao)(dao)體(ti)(ti)有(you)尖端，該處(chu)(chu)附近空(kong)氣(qi)中(zhong)的(de)(de)電(dian)(dian)場強度可變得很(hen)高。當離(li)子(zi)被(bei)吸向導(dao)(dao)體(ti)(ti)時將獲得很(hen)大的(de)(de)加速度，如果這(zhe)些(xie)離(li)子(zi)有(you)條(tiao)件(jian)與空(kong)氣(qi)碰撞，則(ze)會產(chan)生大量的(de)(de)離(li)子(zi)，使空(kong)氣(qi)變得極易導(dao)(dao)電(dian)(dian)而非絕(jue)緣體(ti)(ti)了，同時借電(dian)(dian)暈(yun)(yun)放電(dian)(dian)而加速導(dao)(dao)體(ti)(ti)放電(dian)(dian)。因空(kong)氣(qi)分(fen)子(zi)在碰撞時會發(fa)光(guang)，故電(dian)(dian)暈(yun)(yun)時在導(dao)(dao)體(ti)(ti)尖端處(chu)(chu)能看到亮(liang)光(guang)。

電(dian)(dian)(dian)暈引(yin)起電(dian)(dian)(dian)能(neng)的(de)損耗，并對通信(xin)和廣播傳輸信(xin)號(hao)產(chan)生干擾作(zuo)用。例如，雷雨時(shi)物體(ti)尖端也會(hui)產(chan)生電(dian)(dian)(dian)暈現象，避雷針即(ji)利(li)用了(le)電(dian)(dian)(dian)暈放電(dian)(dian)(dian)中和帶電(dian)(dian)(dian)的(de)云層(ceng)而防止(zhi)雷擊。

標簽：電暈 、