Electricity Worksheet-18
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How will you join three resistances, each of 2 Ω so that the effective resistance is 3 Ω?
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On what factors does the resistivity of a material depend ?
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What happens to the current in a circuit if its resistance is doubled ?
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What happens to the resistance of a circuit if the current through it is doubled ?
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What happens if the potential difference across a resistance is doubled ?
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How does the resistance of a wire depend upon its radius ?
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How does the resistance of a wire depend on its length?
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How does the resistance of a metallic wire depend on its temperature.
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Two wires are of the same length, same radius, but one of them is of copper and the other is of iron. Which will have more resistance ?
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Find the pd required to pass a current of 0.2 A in a wire of resistance 20 Ω.
Answer:
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A parallel combination of two resistances (which will be 1 Ω) joined in series with the third resistance (2 Ω).
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It depends only on the nature of the material.
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The current is reduced to half its previous value.
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The resistance of the circuit does not depend on the current through it.
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The current through the resistance is doubled as I = V/R.
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The resistance of wire, R ∝ 1/r2 where r is the radius of the wire.
(R = Pl/A, i.e., R ∝ 1/A or R ∝ I/ πr2 R ∝ I/r2)
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The resistance of a wire, R ∝ I where l is the length of the wire.
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The resistance of a metallic wire increases with temperature.
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As R = pl/A and p for iron is more than that for copper, so the iron wire has more resistance.
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Ohm's law, V = IR = 0.2 × 20 = 4V.