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  4. An aluminium (resistivity ρ=2.2 × 10-8 Ω- m ) wire of a diameter 1.4 mm is used to make a 4 Ω resistor. The length of the wire is

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Q. An aluminium (resistivity $\rho=2.2 \times 10^{-8} \Omega- m$ ) wire of a diameter $1.4\, mm$ is used to make a $4 \Omega$ resistor. The length of the wire is

EAMCETEAMCET 2007Current Electricity

Solution:

Length of the wire is
$l =\frac{R A}{\rho}$
$\therefore l=\frac{4 \times \pi \times\left(0.7 \times 10^{-3}\right)^{2}}{2.2 \times 10^{-8}}$
$=280\, m$