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dustbus 2013-8-12 02:32 AM

charging by friction

假如有個block moving toward
正常咪有WD against friction既
咁會唔會有charging by friction
跟住再earthing
所以net charge都係0??



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dustbus 2013-8-12 02:40 AM

oh it seems that i have misconception earthing cannot occur in insulator...??



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dustbus 2013-8-12 03:14 AM

oh it seems that i have misconception earthing cannot occur in insulator...??



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thomas1126 2013-8-15 12:24 PM

你應該講得岩,friction可能會remove左block的electron,但係個block因為貼住地面,然後earthing番。
insulator同earthing得快唔快有關,有足夠時間的話應該都會earthing到。

p.s. friction charge 得好少

dustbus 2013-8-15 02:38 PM

[quote]原帖由 [i]thomas1126[/i] 於 2013-8-15 12:24 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369467770&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
你應該講得岩,friction可能會remove左block的electron,但係個block因為貼住地面,然後earthing番。
insulator同earthing得快唔快有關,有足夠時間的話應該都會earthing到。

p.s. friction charge 得好少 [/quote]


咁可唔可以GAIN electron??

thomas1126 2013-8-15 08:29 PM

都得架,remove定gain都係睇個electron去邊姐,可能今次係自己被removed,下次就係remove人地而gain到。


p.s. 不過唔同既material對於gain定loss既probability都唔同

dustbus 2013-8-15 09:16 PM

感謝師兄 請問哩題點做:smile_41::smile_41:

point charge係唔係代表正極??

[[i] 本帖最後由 dustbus 於 2013-8-15 09:18 PM 編輯 [/i]]

thomas1126 2013-8-15 09:27 PM

D? point charge即係一個點咁細既charge,無分正負
x個點: 左同中cancel,得右邊既影響
y個點:左,中,右都有影響 
所以y>x

↗亢龍無悔↙ 2013-8-15 10:31 PM

[quote]原帖由 [i]thomas1126[/i] 於 15-8-2013 09:27 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369501532&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
D? point charge即係一個點咁細既charge,無分正負
x個點: 左同中cancel,得右邊既影響
y個點:左,中,右都有影響 
所以y>x [/quote]
#8 demonstrated an excellent misconception in electric field.



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dustbus 2013-8-15 10:40 PM

[quote]原帖由 [i]thomas1126[/i] 於 2013-8-15 09:27 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369501532&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
D? point charge即係一個點咁細既charge,無分正負
x個點: 左同中cancel,得右邊既影響
y個點:左,中,右都有影響 
所以y>x [/quote]


why direction is opposite

and why x個點: 左同中cancel,得右邊既影響 the point charge have no +ve or -ve

↗亢龍無悔↙ 2013-8-15 11:27 PM

[quote]原帖由 [i]dustbus[/i] 於 15-8-2013 10:40 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369508032&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]



why direction is opposite

and why x個點: 左同中cancel,得右邊既影響 the point charge have no +ve or -ve [/quote]咁所以個答案咁係A囉:smile_04:

dustbus 2013-8-15 11:40 PM

[quote]原帖由 [i]↗亢龍無悔↙[/i] 於 2013-8-15 11:27 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369512793&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
咁所以個答案咁係A囉:smile_04: [/quote]

龍哥求解:Q:Q:Q:Q:Q:Q

thomas1126 2013-8-15 11:52 PM

[quote]原帖由 [i]↗亢龍無悔↙[/i] 於 2013-8-15 10:31 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369507150&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

#8 demonstrated an excellent misconception in electric field.



[img]http://i1.hk/d/images/r10/mobile.jpg[/img] [/quote]
你確定我錯?
唸清楚喎,electric field = electric force/ charge
即係electric field strength 愈大 = electric force愈大
假設全部都係排斥力
咁因為左同中同x係等距,所以力會cancel
y 點就因為左中右都無cancel個力 所以係最大

比你會點解答?

↗亢龍無悔↙ 2013-8-16 12:10 AM

[quote]原帖由 [i]thomas1126[/i] 於 15-8-2013 11:52 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369515324&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

你確定我錯?
唸清楚喎,electric field = electric force/ charge
即係electric field strength 愈大 = electric force愈大
假設全部都係排斥力
咁因為左同中同x係等距,所以力會cancel
y 點就因為左中右都無 ... [/quote]而家係electric field, 唔係問你個magnetice field carried by current flowing out of the page
Electric field strength = force / charge, where the force is given by cxxxxxlum's law

So the final electric strength in certain position should be adding all the strengths produced by all charges

Whether, the strength will be cancelled or not, is determined by the nature of charges

As the question said that the all charges have same nature, the cancellation you mentioned is impossible to happen as E = k . ( Q / r*2 )

The cancellation will only occur if some Q are positive and some are negative

啲AL physics比返呀sir唔係問題,但係都唔好亂咁線人先得嫁

[[i] 本帖最後由 ↗亢龍無悔↙ 於 2013-8-16 12:16 AM 編輯 [/i]]

dustbus 2013-8-16 12:26 AM

我係HKEAA個PHY卷到拎答案=.=

但ANS係D

我初頭都古A:Q :Q

↗亢龍無悔↙ 2013-8-16 12:32 AM

[quote]原帖由 [i]dustbus[/i] 於 16-8-2013 12:26 AM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369518380&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
我係HKEAA個PHY卷到拎答案=.=

但ANS係D

我初頭都古A:Q :Q [/quote]
呵呵,答案係D的話,咁我要道歉,寸錯人 lol



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thomas1126 2013-8-16 12:35 AM

[quote]原帖由 [i]↗亢龍無悔↙[/i] 於 2013-8-16 12:10 AM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369516919&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
而家係electric field, 唔係問你個magnetice field carried by current flowing out of the page
Electric field strength = force / charge, where the force is given by cxxxxxlum's law

So the final electr ... [/quote]
首先我一句都無提過magnetic野,
你呢幾句都仲係岩
Electric field strength = force / charge, where the force is given by coulomb's law

So the final electric strength in certain position should be adding all the strengths produced by all charges

Whether, the strength will be cancelled or not, is determined by the nature of charges
但去到cancellation個度,呢度最關鍵, 就係因為same nature

所以先可以cancel到你要留意到"左"係x左邊 "中"係x右邊,而且距離一樣,所以cancel到,

我唸你會唔會搞錯左要一正一負cancel到

就好似地球同月亮都係"引力",所以中間先有一個點係cancel到0引力

可能我係錯既,但你說服唔到我

另外補充番 point charge無分正負意思係,可以係正又可以係負,要題目比先知,而家佢淨係講q 所以唔知

direction opposite係因為,假設你當佢係斥力,
咁x個點會比右推向左
y個點就比左中右推向右

[[i] 本帖最後由 thomas1126 於 2013-10-6 12:59 AM 編輯 [/i]]

dustbus 2013-8-16 12:47 AM

兩位師兄都好勁:smile_35: :smile_35: 感激不盡


我以為同CHARGE就個direction就一樣

原來係睇粒野點行:@:@:@


BTW書都有講同CHARGE既,中間個E fleid會=0

THX ALL CHING

[[i] 本帖最後由 dustbus 於 2013-8-16 01:02 AM 編輯 [/i]]

jmlo 2013-8-16 03:42 AM

回覆 18# 的帖子

Indeed, the situation is better understood if you recall electric field is a vector quantity which carries both direction and magnitude. The actual electric field at a position (e.g. point X in the question) is simply the vector sum of the fields due to the point charges.

↗亢龍無悔↙ 2013-8-16 08:37 AM

[quote]原帖由 [i]dustbus[/i] 於 16-8-2013 12:47 AM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369519983&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
兩位師兄都好勁:smile_35: :smile_35: 感激不盡


我以為同CHARGE就個direction就一樣

原來係睇粒野點行:@:@:@


BTW書都有講同CHARGE既,中間個E fleid會=0

THX ALL CHING [/quote]
教錯人仲要聲大夾惡係到鬧人,記得save低我啲犯罪証據



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thomas1126 2013-8-16 09:52 AM

都係clarify番姐,無咩所謂



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↗亢龍無悔↙ 2013-8-16 11:03 AM

我當左electric potential 咁加哂所有野
唔記得左field strength係vector



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dustbus 2013-8-16 05:08 PM

人有失手姐…… 題題岩曬咩唔通  龍哥你本身係勁底嘛



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↗亢龍無悔↙ 2013-8-16 06:25 PM

[quote]原帖由 [i]dustbus[/i] 於 16-8-2013 05:08 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369561774&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]
人有失手姐…… 題題岩曬咩唔通  龍哥你本身係勁底嘛



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最勁扮勁寸人麻



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dustbus 2013-8-16 08:41 PM

[quote]原帖由 [i]↗亢龍無悔↙[/i] 於 2013-8-16 06:25 PM 發表 [url=http://www.discuss.com.hk/redirect.php?goto=findpost&pid=369566789&ptid=22298275][img]http://www.discuss.com.hk/images/common/back.gif[/img][/url]

最勁扮勁寸人麻



[img]http://i1.hk/d/images/r10/mobile.jpg[/img] [/quote]
=.=龍哥你平時都教左我好多題:Q:Q你真係勁
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