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![[Post New]](/templates/default/images/icon_minipost_new.gif) 28 Apr 2008 20:42:20 IST
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its written that temp. of unknown resistance is increased,is it necessary that res. will also increase?
wat if alfa is negative coz it aint given that its a mettalic resistor
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28 Apr 2008 20:49:38 IST
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http://en.wikipedia.org/wiki/Electrical_resistance#In_semiconductors_and_insulators
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28 Apr 2008 21:25:23 IST
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hey !
I know that alpha can be -ve too, but the given question is on meter bridge, and we never use semiconductors in meter bridge, do we ?
I hope u got it !
rate me if found useful !
thanks !
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Umang |
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28 Apr 2008 23:39:44 IST
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hey but y cant we use a semiconductor?? in the question its only given"unknon resistor" and not "mettalic resistor"
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29 Apr 2008 19:37:38 IST
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hey !
first u tell me what is the purpose of meter bridge ?
if u understand that, u will get that.
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Umang |
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29 Apr 2008 19:49:51 IST
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@ UMANG...........
U R VERY CRT ITZ HARD TO CONVINCE SOCCIBOY........
METER BRIDGE IS THE EXPERIMENT USED TO DETERMINE RESISTANCE OF UNKWN CONDUCTORS N NOT SEMICONDUCTORS...............
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lighten up the darkness............
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29 Apr 2008 23:22:00 IST
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is that definition given in a book or smtn? coz in wiki its given that a w.stone bridge's used to measure unknown "electrical" resistance.
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29 Apr 2008 23:33:05 IST
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meter bridge works on principle of wheatstone bridge where the resistances and/or wire lengths are proportional.. semi conductors would obviously spoil the relation.
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---------------------------------------------------------------
* Gaurav Ragtah ( aka Artemis Fowl )
* Agent 'G' [sniper] - SD-6 (Alliance of Twelve)
  
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29 Apr 2008 23:37:11 IST
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how?
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29 Apr 2008 23:47:48 IST
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the wires are made of normal metal material...
constantin or manganin alloys
their resistance increases on heating
so if u use semiconductors whose resistance decreases on heating, the proportionality will not b mantained so the wheatstone principle wont b followed so how will u measure
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---------------------------------------------------------------
* Gaurav Ragtah ( aka Artemis Fowl )
* Agent 'G' [sniper] - SD-6 (Alliance of Twelve)
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29 Apr 2008 23:55:39 IST
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i dnt get it man,wat do u mean by proportionality wnt be mantained?
see its given that can null point remain same if we decrease the known resistance and increase the temp. of unknown resist.
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29 Apr 2008 23:58:01 IST
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whenever we talk of wheatstone bridge and meter bridge we talk of standard resistances not semi conductors
for semi conductors we use PN junction box to determine the resistance.
it is self understood. a standard rule.
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---------------------------------------------------------------
* Gaurav Ragtah ( aka Artemis Fowl )
* Agent 'G' [sniper] - SD-6 (Alliance of Twelve)
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30 Apr 2008 00:03:36 IST
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ok i understand.but WAT IFF by chance i put a semiconductor can the null point be obtained?
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30 Apr 2008 00:08:31 IST
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well the slopes of resistance versus temperature graphs of metallic and semi conductor resistances are not the same so null point will not remain same
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---------------------------------------------------------------
* Gaurav Ragtah ( aka Artemis Fowl )
* Agent 'G' [sniper] - SD-6 (Alliance of Twelve)
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30 Apr 2008 00:09:36 IST
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