Question

粗細(xì)均勻的電熱絲放入水中，通電10min水開始沸騰；若將電阻絲對(duì)折并聯(lián)后放入同一壺水中，通電到水開始沸騰，所需要的時(shí)間是（不計(jì)一切熱損失）（ ）
A．2.5min
B．5min
C．20min
D．40min

Answer 1

【答案】分析：電阻絲對(duì)折后電阻變?yōu)樵瓉淼?img src="http://thumb.1010pic.com/pic6/res/czwl/web/STSource/2013102409042713793696/SYS201310240904271379369005_DA/0.png">，利用公式Q=W=Pt=t，進(jìn)行分析．
解答：解：電阻絲對(duì)折后電阻變?yōu)樵瓉淼?img src="http://thumb.1010pic.com/pic6/res/czwl/web/STSource/2013102409042713793696/SYS201310240904271379369005_DA/2.png">，根據(jù)公式P=，功率變?yōu)樵瓉淼?倍，故燒開相同一壺水所需時(shí)間變?yōu)樵瓉淼?img src="http://thumb.1010pic.com/pic6/res/czwl/web/STSource/2013102409042713793696/SYS201310240904271379369005_DA/4.png">，t′=t=×10min=2.5min．
故選A．
點(diǎn)評(píng)：本題考查了電熱的計(jì)算公式，關(guān)鍵是選擇好對(duì)應(yīng)的公式．