Resistivity Flashcards – AQA A-level Physics (7408)

What is electrical resistivity?

A material property describing how strongly the material opposes electric current.

What is the formula for the resistivity of a uniform conductor in terms of its resistance $R$, cross-sectional area $A$ and length $L$?

$\rho = \frac{RA}{L}$

For a given resistivity, how does a conductor’s resistance depend on its length and cross-sectional area?

Resistance increases with length and decreases with cross-sectional area.

What is the SI unit of electrical resistivity?

The ohm metre, $\Omega\,\mathrm{m}$.

How can temperature affect a material’s electrical resistivity?

Resistivity can depend on temperature.

What is a negative temperature coefficient (NTC) thermistor?

A temperature-sensitive resistor whose resistance decreases as its temperature increases.

Why does an NTC thermistor's resistance decrease when it is heated?

Heating increases the number of charge carriers available to conduct in its semiconductor material.

What is the general shape of an NTC thermistor's resistance–temperature graph?

It slopes downward and is generally non-linear.

How can an NTC thermistor act as a temperature sensor?

A temperature change produces a resistance change that can be measured or used by a circuit to indicate temperature.