1.

यदि किसी तार को खींचकर उसकी लम्बाई दोगुनी कर दी जाये , तो उसका प्रतिरोध कितना हो जायेगा ?

Answer» ` :. pir_(1)^(2)l_(1) = pir_(2)^(2)l_(2)`
या ` (l_(1))/(l_(2))=((r_(2))/(r_(1)))" "`…(1)
सूत्र `R=(rhol)/(A)` से
` (R_(1))/(R_(2))=(l_(1))/(A_(1)) xx (A_(2))/(l_(2)) = (l_(1))/(l_(2)) xx (pir_(2)^(2))/(pir_(1)^(2))`
या ` (R_(1))/(R_(2)) =(l_(1))/(l_(2)) xx(r_(2)^(2))/(r_(1)^(2))`
समी (1 ) में मान रखने पर ,
`(R_(1))/(R_(2))=((l_(1))/(2l_(1)))^(2)=1/4`
या `R_(2) = 4R_(1)`


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