A copper wire with a cross-sectional area of $1.0\ \text{mm}^2$ carries a steady current of $2.72\ \text{A}$. Copper has $8.5 \times 10^{28}$ free electrons per cubic metre, and the charge of an electron is $1.6 \times 10^{-19}\ \text{C}$. The drift speed of the electrons is