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Unit 2 Electricity and Light

Quick questions on Resistance: Ohm's law, I-V graphs and resistivity - WJEC A-Level Physics

4short Q&A pairs drawn directly from our worked dot-point answer. For full context and worked exam questions, read the parent dot-point page.

What is resistivity?
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Resistivity ρ\rho is a property of the material (in ohm metres). Resistance increases with length and decreases with cross-sectional area. Measuring the resistivity of a wire is a specified practical: plot RR against LA\dfrac{L}{A} and the gradient is ρ\rho.
What is effect of temperature?
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In a metal, raising the temperature makes the lattice ions vibrate more, scattering electrons and increasing resistance. In a semiconductor (such as a thermistor), warming releases more charge carriers, so resistance falls.
What is q1?
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A wire of length 2.0 m2.0\,\text{m} and cross-sectional area 5.0×10−7 m25.0\times10^{-7}\,\text{m}^2 has resistance 1.8 Ω1.8\,\Omega. Find its resistivity. [2 marks]
What is q2?
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Explain why the resistance of a metallic conductor rises with temperature. [2 marks]

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