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When an iron wire of diameter 1 cm is copper plated uniformly. Resistance of iron reduces to 1/3 of its original value. Calculate the thickness of copper plating, Resistivities of copper and iron are 1.8 times 10^-6 Omega.cm and 1.98 times 10^-5 Omega.cm respectively. |
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Answer» Solution :Let RESISTANCE of iron wire be r and that of copper plating x. As they are in PARALLEL, so equivalent resistance , `R_(eq)=(rx)/(r+x)` `therefore(rx)/(r+x)=r/3or,3rx=r^2+rxor,2rx=r^2` `therefore x=r/2` Now, `r=rhol/A=(1.98times10^-5timesl)/(pi(0.5)^2)` Similarly , `x=(1.8times10^-6timesl)/(2pi(0.5)d)` (l=length , d= thickness) SOLVING for r and x, it is observed that d=0.045 (approx) |
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