27. Resistors & DC Circuits

A 0.65-mm-diameter copper wire carries a tiny current of 3.2 μA. Estimate the electric field in the wire.

A 5.30-m length of 2.0-mm-diameter wire carries a 750-mA current when 22.0 mV is applied to its ends. If the drift speed is 1.7 x 10^-5 m/s, determine the resistivity ρ.

At a point high in the Earth’s atmosphere, He²⁺ ions in a concentration of 2.8 x 10¹²/m³ are moving due north at a speed of 2.0 x 10⁶ m/s. Also, a 7.0 x 10¹¹ / m³ concentration of O⁻₂ ions is moving due south at a speed of 6.2 x 10⁶ m/s. Determine the magnitude and direction of the current density $\overrightarrow{j}$ at this point.