Define the ohm as the unit used for electrical resistance.
Determine the SI base units that correspond to resistivity.
A cell with e.m.f. $2.0\text{ V}$ and negligible internal resistance is linked to a variable resistor $R$ and a metal wire, as shown in Fig. 5.1. The wire measures $900\text{ mm}$ in length and has a cross-sectional area of $1.3 \times 10^{-7}\text{ m}^2$. Its resistance is $3.4\,\Omega$. Calculate the resistivity of the metal wire.
The resistance of $R$ can be changed from $0$ to $1500\,\Omega$. Calculate the largest potential difference (p.d.) and the smallest p.d. that can occur across the wire.
Calculate the power transformed in the wire when the p.d. across the wire is $2.0\text{ V}$.
Resistance $R$ in (c) is now replaced by another variable resistor $Q$. State the power transformed in $Q$ when $Q$ has zero resistance.
Resistance $R$ in (c) is now replaced by another variable resistor $Q$. State the power transformed in $Q$ when $Q$ has infinite resistance.