128 Chapter 6 • Electricity
7. Calculate the resistance of a conductor 30 metres long. Te cross-sectional area of the conductor is 12,57 × 10–6 m2 and the resistivity of the conductor is 1,725 × 10–8 ohm metres.
8. Calculate the resistance of a copper conductor with a length of 10 m and a cross-sectional area of 12,5 × 10–6 m2. Take the resistivity of copper as 1,725 × 10–8 ohm metres.
(0,041 17 ohms) (0,0138 Ω)
9. Calculate the resistance of a copper conductor with a cross-sectional area of 1,8 × 10–6 m2 and a length of 1 200 m. Take the resistivity of copper as 0,017 25 micro-ohm metre.
10. Te resistance of a copper conductor is 10 ohms. Calculate the length of the conductor if the cross-sectional area is 10 × 10–6 m2 and the specific resistance of the copper is 0,017 24 × 10–6 ohm metre.
(11,5 ohms) (5 800 m or 5,8 km)
11. Calculate the resistance of a copper conductor with a cross-sectional area of 1,767 × 10–6 m2 and a length of 40 meters. Take the resistivity of copper as 1,725 × 10–8 ohm metres.
12. Calculate the resistance of a copper conductor with a cross-sectional area of 12,57 mm2 and a length of 6 200 mm. Te specific resistance of the copper is 1,724 × 10–8 ohm metres.
(0,39 ohms) (0,008 5 ohms)
13. Calculate the resistance of an aluminium conductor with a cross-sectional area of 28,27 mm2 and a length of 750 m. Take the resistivity of aluminium as 0,016 micro-ohm metre.
14. Calculate the resistance of an aluminium conductor if it has a cross-sectional area of 1,5 mm2 and a length of 100 m. Take the resistivity as 0,016 micro-ohm metre.
15. Calculate the resistance of a copper conductor with a cross-sectional area of 3,14 × 10–6 m2 and a length of 600 metres. Te specific resistance of the copper is 0,0172 µΩm.
(0,424 5 ohms) (1,067 ohms) (3,285 ohms)
16. If 450 metres of nichrome wire has a resistivity of 1,1 micro-ohm metres and a cross-sectional area of 6,5 × 10–5 m2, find its resistance.
(7,615 ohms)
17. What would the resistance of an element be if it is wound with 15 metres of resistance wire which has a cross-sectional area of 0,03 mm2 and a resistivity of 1,7 × 10–8 ohm metres?
(8,5 ohms)
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