Consider a strip of material that has a rectangular crosssection with height \(310 \mu \mathrm{m}\) and width \(4.2 \mathrm{~mm}\) and which carries a uniform current of \(5.5 \mathrm{~mA}\).

(a) What is the current density in the strip?

(b) If the number density of the charge carrier (conduction electron) is \(3.5 \times 10^{23} \mathrm{~m}^{-3}\), then calculate the drift speed in the strip.