Electricity Worksheet-5
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The resistance of a wire of length 80 cm and of uniform area of cross-section 0.025 cm2, is found to be 1.50 ohm. Calculate the resistivity of the wire.
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Calculate the resistance of 1 km long copper wire of radius 1 mm. Resistivity of copper is 1.72 × 10–8 Ω m.
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Two copper wires A and B of length 30 m and 10 m have radii 2 cm and 1 cm respectively. Compare the resistances of the two wires. Which will have less resistance?
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A 4 Ω wire is doubled on it. Calculate the new resistance of the wire.
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What should be the length of a nichrome wire of resistance 4.5Ω, if the length of a similar wire is 60 cm and resistance 2.5Ω?
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A negligibly small current is passed through a wire of length 15 m and of uniform cross-section 6.0 10–7 m2 and its resistance is measured to be 5.0Ω. What is the resistivity of the material at the temperature of the experiment?
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A metal wire of resistivity 64 10–6 ohm cm and length 198 cm has a resistance of 7Ω. Calculate its radius.
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Calculate the resistivity of the material of a wire 1.0 m long, 0.4 mm in diameter and having a resistance of 2.0Ω.
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The resistivity of copper is 1.76 × 10–8 ohm m. The radius of the wire is 1 mm. Calculate the length of a telegraph wire needed for having a resistance of 10.5 Ω.
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A resistance wire made from German silver has a resistance of 4.25 Ω. Calculate the resistance of another wire made from the same material such that its length increases by 4 times and area of cross-section decreases by 3 times.
Answer:
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length of the wire, l = 80 cm
Cross-sectional area of the wire, A = 0.025 cm2
Resistance of the wire, R = 1.50 Ω
As ohm cm
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Length of the wire, l = 1 km = 1000 m
Radius of the wire, r = 1 mm = 10–3 m, resistivity of copper,
Cross-sectional area of the wire,
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Let the two resistances be labeled as R1 and R2.
Here,
As
and
Thus,
Clearly, R1 < R2
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When the wire of length l and cross-sectional area A is doubled on it, its length becomes l/2 and cross-sectional area becomes 2A.
New resistance of the wire,
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= 0.024 cm
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As
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