Electric Currents & Ohm's Law - Units of Resistivity example 4
Question : Calculate the resistance of 1 km long cable composed of 19 stands of similar copper conductors, each strand being 1.32 mm in diameter. Allow 5% increase in length for the ‘lay’ (twist) of each strand in completed cable. Resistivity of copper may be taken as 1.72 × 10−8 Ω-m.
Solution :
Allowing for twist, the length of the stands.
= 1000 m + 5% of 1000 m = 1050 m
Area of cross-section of 19 strands of copper conductors is
19 × π × d2/4 = 19 π × (1.32 × 10−3)2/4 m2
Now,
= 0.694 Ω
Read article – Units of Resistivity
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