calculate the resistance of 1 km long copper wire of radius 1mm resisitivity  of the copper is 1.72 *18 - 8 -ohm - meter 

Dear Student ,
We know that the resistance is given as

R = ρL/A

here,

ρ = 1.72 x 10-8 ohm.m

L = 1000 m

A = πr2 = π(0.5x10-3)2 = 7.85 x 10-7 m2

so,

R = ( 1.72 x 10-8 x 1000 ) / 7.85 x 10-7 

thus, resistance of the wire will be

R = 21.91 Ω

Regards

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