A horizontal metal strip \(1.0 \mathrm{~mm}\) thick and \(20 \mathrm{~mm}\) wide carries a 20-A current along its length, and both the length and the width are perpendicular to a uniform magnetic field of magnitude \(2.0 \mathrm{~T}\) that is directed vertically up. The potential difference across the strip width is \(4.27 \mu \mathrm{V}\). No external voltage is applied to the strip.

(a) If the side of the strip width that is to your left as you look in the direction of the current is at the higher potential, what is the sign of the mobile charge carriers? What are 

\((b)\) the speed and 

\((c)\) the number density of the charge carriers?