A long, straight wire with a cross-sectional area A carries a current i . Suppose the number of free electrons per unit volume is n . An observer is positioned on a trolley that travels in the direction opposite to the current at a speed v = i nAe , keeping a separation distance r from the wire. The magnetic field observed by this person is approximately

Step-by-step solution

The drift velocity of free electrons in the wire is given by v_d = i nAe . The direction of the drift velocity of electrons is opposite to the direction of the conventional current. The trolley moves in the direction opposite to the current with speed v = i nAe , which is exactly equal to the drift velocity of the electrons. In the reference frame of the trolley, the free electrons are at rest, so they do not contribute to the current. However, the positive ions of the metallic lattice, which are stationary in the