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ͬײǵԵģСõٶȡ
ͼ2.16ϰ2.18ͼ̲ͼ2.37
ѡ˺СΪϵײǵԵģϵĻеغ㡣ˮƽΪ㣬˰ֱλõδСײʱĽٶΪ?
mgL?11J?2?mgL 22ڸСײУϵOĽǶغ㡣ײ˵Ľδ??
J??J???mvL
ʽJ?mL3ΪOתvΪСõٶȡɻеغ㣬
2111J?2?J??2?mv2 2221ʽɽСõٶv?3gL
2
3.3 ͼ3.2ʾһαƬϸţİ뾶ΪRڰ뾶ΪR/2еQȷֲڻϣϸ3RҲеQȷֲϣԲOĵ糡ǿ Բϸӳϣ
ͼ3.2ϰ3.3ͼڽ̲ͼ3.33ϼӣ
ԲϵĵɶԲOԳƷֲOijǿΪ㣬ϳǿϸϵĵOijǿѡϸΪԭ㣬ֱΪxᡣxȡһ
Ԫdq??dx?Qdx3ROijǿΪ
dE?dqQdx?
4??0(4R?x)212??0R(4R?x)2ϸϵĵOijǿΪ
E?ֱ¡˼
3.11ͼ3.10ʾڵܶΪ?ľȴУһοǻOָοǻO?ʸaʾ֤οǻһ糡ǿΪ
12??0R?0Q3RdxQ? 22(4R?x)16??0RE?
?a 3?0ͼ3.10ϰ3.11ͼڽ̲ͼ3.39ϼӣ
֤ οǻԿɵܶȷֱΪ???ľȴСӶɡǻһPijǿɱʾΪ E?E1?E2?????r1?r2?(r1?r2) 3?03?03?0E1E2ֱΪСPijǿɼιϵr1?r2?aʽд
E?֤
?a 3?03.12뾶ΪbϸԲԲOxyϵԭϡԲɵܶ
??acos?aΪͼ3.11ʾԲĴ糡ǿȵxy
ͼ3.11ϰ3.12ͼڽ̲ͼ3.40ϼӣ
d? dE b dq
ڵɷֲ??acos?xԳƣԲO㴦Ey?0ǿxᡣȡԪdq??bd?Ox᳡ǿΪ
acos2?d??bd?cos? dEx?? ??24??0b4??0bֵ
2? Ex??dEx??0a4??0b2?2cos??d???0a4?0b
3.13 ͼ3.12ʾеŵɵͬԲ棬뾶ֱΪR1
R2(R2>R1)λϵĵΪ?Ϊrĵ糡ǿȣ(1)r?R1
(2)R1?r?R2(3)r?R2
ͼ3.12ϰ3.13ͼڽ̲ͼ3.41ϼӣ
R1 R2 ԳƷֲ˵糡ķֲԳԡΪrλȵ
ͬԲθ˹棬ݸ˹ E2?r?qΪ˹Χĵɡ (1) r?R1q?0E1?0 (2)R1?r?R2q??E2?(3)r?R2q?0E3?0
3.14q?10?9q?0
? 2??0rCͬһֱϵABCֱqΪ10cm20cm
30cmͼ3.13ʾѡBΪ㣬ACĵUAUC
ϵѡȡͼʾxA?10cmxB?20cmxC?30cmBΪ㡣ɵƵĶ壬
xBx
ͼ3.13ϰ3.14ͼ
0
UA?xA?4??q0x2dx?q4??0(11?) xAxB10?9112?(?)?10?45V ??1210204??8.85?10xBUC?xC?4??q0x2dx?q4??0(11?) xCxB10?9112?(?)?10??15V ??1230204??8.85?103.18ͼ3.16ʾ뾶ֱΪR1 R2
ȴ籡ͬķãR1< R2֪Ǽ
ͼ3.16ϰ3.18ͼ
̲ͼ3.45