A copper wire of length 1 m and rad...
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A copper wire of length 1 m and radius 1 mm is joined in series with an iron wire of length 2 m and radius 3 mm and a current is passed through the wires. The ratio of the current density in the copper and iron wires is (a)2:3 (b) 6:1 (c)9:1 (d) 18:1 Comalou

JEE/Engineering Exams
Physics
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Wrent density ( J=frac{i}{A}=frac{i}{pi r^{2}} ) ( Rightarrow frac{J_{1}}{J_{2}}=frac{i_{1}}{i_{2}} times frac{r_{2}}{r_{1}^{2}} ) But wives ( m_{l} ) in seles, ( 5 pi i=i_{2} ) ( S_{0} frac{I_{1}}{5_{2}}=frac{r_{2}^{2}}{r_{1}^{2}}=frac{3^{2}}{1^{2}}=frac{q}{1}=9: 1 )
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