Question 303: Current Electricity

Question

What equal length of an iron wire and a copper-nickel alloy wire, each of 2 mm diameter connected parallel to give an equivalent resistance of 3$$\Omega$$ ?
(Given resistivities of iron and copper-nickel alloy wire are 12 $$\mu$$$$\Omega$$ and 51 $$\mu$$$$\Omega$$ cm respectively)

Accepted Answer

$${{{R_1}{R_2}} \over {{R_1} + {R_2}}} = 3$$
$${{{{(12 	imes {{10}^{ - 6}} 	imes {{10}^{ - 2}})} \over {\pi {{(2)}^2} 	imes {{10}^{ - 6}}}} 	imes {{(51 	imes {{10}^{ - 6}} 	imes {{10}^{ - 2}})l 	imes 4} \over {\pi {{(2)}^2} 	imes {{10}^{ - 6}}}}} \over {{{63 	imes {{10}^{ - 6}} 	imes {{10}^{ - 2}} 	imes l 	imes 4} \over {\pi {{(2)}^2} 	imes {{10}^{ - 6}}}}}}$$ = 3
$$\Rightarrow$$ l = 97 m

Answer

82 m

Answer

97 m

Answer

110 m

Answer

90 m

Current Electricity

What equal length of an iron wire and a copper-nickel alloy wire, each of 2 mm diameter connected parallel to give an equivalent resistance of 3$\Omega ? (Given resistivities of iron and copper-nickel alloy wire are 12 \mu\Omega and 51 \mu\Omega$ cm respectively)

Choose the correct answer: