An unknown wire in a circuit has a circular cross-section with diameter 2.5 mm. It carries a current of &.7 mA. Part (a) What is the current density, in milliamperes per square centimeter, in this wire? Part (b) If you assume the drift velocity in this wire is 1 x 102 cm/s, what is the density of charge carriers per cubic centimeter? Part (c) If the conductivity in this wire is 2.5 x 106 2 m, what is the average time between collisions, in nanoseconds?