[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-108-1-fire-science-015":3},{"subject":4,"subjectSlug":5,"subjectKicker":6,"subjectShort":7,"question":8,"related":27,"sameNumber":52,"hasEssay":26},"火災學概要","fire-science","火災學 · Fire Science","火災學",{"id":9,"webId":10,"year":11,"session":12,"subject":4,"number":13,"stem":14,"options":15,"answer":20,"answerNote":21,"images":22,"imagesPending":23,"lawTimestamp":11,"explanation":24,"explanationDeep":25,"freq":12,"indexable":26},"fire-108-1-火災學概要-015","fire-108-1-fire-science-015",108,1,15,"下列何種現象對於局部電阻所產生的效應恰與其他三者相反？",{"A":16,"B":17,"C":18,"D":19},"氧化亞銅增殖","開關接觸不良","半斷線","金原現象","D",null,[],false,"本題考點：各種電氣局部發熱現象對電阻的作用方向,辨識何者使該處電阻下降。\n【正解理由】氧化亞銅增殖、開關接觸不良、半斷線三者都是導電路徑劣化,使該處電阻升高,依焦耳定律 P = I²R 在局部產生異常發熱;金原現象則相反,是有機絕緣材料長期受熱而逐步碳化、石墨化,使原本的絕緣體轉變為具導電性的通路,該處電阻是下降而非上升。作用方向與其他三者相反者為金原現象,故選 D。\n【逐項排除】\n(A) 屬電阻上升型。銅導體接觸面氧化生成氧化亞銅(Cu2O)半導體層,接觸電阻升高而發熱,熱又促使氧化亞銅持續增殖,形成惡性回饋。\n(B) 屬電阻上升型。開關接點因磨耗、鬆動、積垢或氧化膜使有效接觸面積減少,接觸電阻升高,通電時熱量集中於接點。\n(C) 屬電阻上升型。導線素線部分斷裂後由剩餘素線承擔全部電流,該段有效截面積變小、電阻變大,反覆彎折處因而過熱。\n(D) 屬電阻下降型,為本題應選者。絕緣材料碳化後形成導電通路,電流沿碳化路徑流動,該處電阻逐步降低。\n【記憶點】三個把電路變窄使電阻變大,金原現象把絕緣體變成導線。","電氣火災的成因在考試上習慣分成兩大群:一群是電流異常(短路、地絡、過負載),一群是局部電阻異常發熱(接觸不良、半斷線、氧化亞銅增殖、積污導電、金原現象)。本題問的正是第二群內部的方向差異,而不是發熱與否——四者都會發熱,差別在於發熱是來自電阻變大還是絕緣變差。\n電阻上升型的物理很單純:焦耳定律 P = I²R,電流固定時電阻越大、單位時間發熱越多,而發熱又加速劣化。氧化亞銅增殖是其中最典型的正回饋:銅在約 200℃ 以上與空氣中的氧生成氧化亞銅,這種半導體具有負電阻溫度係數,溫度升高後其自身導電性改善但接觸界面持續增厚,反覆的加熱與氧化使增殖層不斷擴大,最終在無任何過負載的情況下也能達到起火溫度。半斷線的關鍵是有效截面積:七股絞線斷了五股,剩餘兩股承擔全部電流,該處電流密度暴增,常見於反覆彎折的延長線與插頭根部。\n電阻下降型則屬絕緣劣化。金原現象指有機絕緣材料在長期低溫加熱下逐漸熱分解,揮發成分散失後留下碳,碳含量提高至一定程度即形成連續的導電路徑,絕緣電阻由數百 MΩ 降到數 kΩ,微小漏電流沿路徑流動並持續加熱,形成不可逆的惡化。易混淆的是積污導電現象(tracking):它發生在絕緣表面,由濕氣與塵埃形成導電膜後產生微小放電,逐步碳化出樹枝狀軌跡,兩者結果相似,但金原現象源於長期受熱、積污導電源於表面污染與吸濕。\n相關考點包括火災調查時的痕跡判別:短路痕與熔痕用於判定通電與起火先後,碳化導電路徑則是判定金原現象與積污導電的依據。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-108-1-fire-science-014","依 Thomas 閃燃公式（Thomas Flashover Correlation），有關室內火災發生閃燃所需最小釋熱率，下列敘述何者錯誤？",14,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-108-1-fire-science-016","某發生火警的大樓，室內外溫度分別為 800℃與 20℃，中性帶位於 4 樓；6 樓的內外壓差為 60 Pa，若不考慮外部風等其他因素，則 8 樓的內外壓差約為若干 Pa？",16,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-108-1-fire-science-013","比較室內火災閃燃（Flashover）與複燃（Backdraft），下列敘述何者正確？",13,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-108-1-fire-science-017","危害物質可能因混合儲存或載運而衍生危險，則下列那兩類公共危險物品於混合載運時的危險性最低？",17,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-108-1-fire-science-012","建築物之中性帶高度受室內溫度、室外溫度及上下開口的影響，下列敘述何者錯誤？",12,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-108-1-fire-science-018","當氣體進行「壓縮比=2」的斷熱壓縮時，下列對該氣體的敘述何者正確？",18,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-111-1-fire-science-015",111,"下列發火源在理化現象歸類上，何者與其他不同類別？",{"webId":58,"year":59,"stem":60,"number":13},"fire-110-1-fire-science-015",110,"下列有關液化天然氣（LNG）與液化石油氣（LPG）之比較，何者正確？",{"webId":62,"year":63,"stem":64,"number":13},"fire-109-1-fire-science-015",109,"下列海龍替代滅火藥劑，何者之化學組成為五氟乙烷？",{"webId":66,"year":67,"stem":68,"number":13},"fire-107-1-fire-science-015",107,"有一火場之消光係數為 2 m-1，請問發光物體之能見度為多少公尺？",{"webId":70,"year":71,"stem":72,"number":13},"fire-106-1-fire-science-015",106,"粉塵爆炸與可燃性氣體相同，亦須存在有「最小發火能量」始可能引起粉塵爆炸，下列有關粉塵爆炸「最小發火能量」之敘述何者錯誤？",1785123163188]