Resistivity and conductionEdexcel A-Level Physics: Flashcards

What these 13 flashcards ask

State the equation relating resistance to resistivity.
What is the unit of resistivity?
What is the area of a wire of diameter d?
Doubling a wire's diameter has what effect on its resistance (same length and material)?
State the equation for current in terms of charge carriers.
What do n, q, v and A stand for in I = nqvA?
Why is the drift velocity in a metal very small?
Why does a lamp light almost instantly although drift velocity is tiny?
Why do insulators have a very high resistivity?
Why does a semiconductor have a higher resistivity than a metal?
In the resistivity practical, what do you plot and what is the gradient?
Why use a micrometer and several diameter readings in the practical?
Why use a small current in the resistivity practical?

Exam questions on Resistivity and conduction

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
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
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

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).