An aluminium cable of diameter 4 x 10^-3m and resistivity 3.0 x 10^-8\(\omega\)m has a resistance of 21\(\Omega\). Calculate the length of the cable. (\(\pi = 3.14\))

8.0 x 10²m

8.8 x 10³m

8.0 x 10⁴m

8.8 x 10⁴m

Correct answer is B

R = \(\frac{4eL}{\pid^2}\)

L = \(\frac{R\pid^2}{4e}\)

= \(\frac{21 \times 3.14(4 \times 10^{-3})^2}{4 \times 3.0 x 10^{-8}}\)

= 8.8 x 10³m

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An aluminium cable of diameter 4 x 10-3m and resistivity 3.0 x 10-8\(\omega\)m has a resistance of 21\(\Omega\). Calculate the length of the cable. (\(\pi = 3.14\))