Resistivity and conductionEdexcel A-Level Physics: Mind map

Exam questions on Resistivity and conduction

1. A cable manufacturer draws copper into uniform wire of diameter 0.50 mm. The resistivity of copper at room temperature is 1.7 × 10⁻⁸ Ω m. A length of 2.0 m of this wire is used as a test sample.
   A second wire of the same copper has twice the diameter and twice the length of the sample. Calculate its resistance.2 marks
2. A copper wire of cross-sectional area 1.0 × 10⁻⁶ m² carries a steady current of 3.0 A. Copper has 8.5 × 10²⁸ conduction electrons per cubic metre.
   The drift velocity is very small, yet a lamp connected to this wire lights almost immediately when the switch is closed. Explain why.2 marks
3. In a core practical a student determines the resistivity of nichrome wire. She measures the diameter of the wire with a micrometer, then connects different lengths l of the wire into a circuit and measures the p.d. across each length and the current in it. She plots resistance R against length l, and the gradient of her best-fit line is 13.4 Ω m⁻¹. Her mean diameter for the wire is 0.32 mm.
   Calculate the resistivity of nichrome from the student's results.3 marks