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Asked by saharanmanish44 | 03 Oct, 2023, 07:43: PM
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Resistance R = ρ × ( L / A ) , where ρ is resistivity , L is length of wire and A is area of cross section of wire.
 
If resistance of given wire is 1 Ω , then begin mathsize 14px style R space equals space rho space cross times L over A end style = 1 Ω
If wire is stretched so that length L is increased to 1.25 L , then cross section area  becomes ( A/1.25)  because volume of wire is constant .
 
If length increases then area decreases by same proportion .
 
New resistance R' is
 
begin mathsize 14px style R apostrophe space equals space rho space cross times space fraction numerator L apostrophe over denominator A apostrophe end fraction end style = begin mathsize 14px style rho space cross times space fraction numerator 1.25 space L over denominator left parenthesis space A space divided by space 1.25 right parenthesis end fraction space equals space left parenthesis 1.25 right parenthesis squared space rho space cross times L over A space equals space 1.5625 space R end style
Increase in resistance is 56 %
Answered by Thiyagarajan K | 04 Oct, 2023, 08:01: AM

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