10. In moving four times as far away from a cyrrent-carrying conductor, the density of the flux lines will have __ by FOPUfour times.

The magnetic field strength (and thus the flux density) around a long, straight, current-carrying conductor is inversely proportional to the distance from the conductor. This relationship is described by Ampere's Law and, for a long straight wire, results in the equation:<br /><br />B = (μ₀ * I) / (2π * r)<br /><br />Where:<br /><br />* B is the magnetic field strength (or flux density)<br />* μ₀ is the permeability of free space (a constant)<br />* I is the current<br />* r is the radial distance from the wire<br /><br />If the distance (r) is increased by a factor of four (i.e., quadrupled), the magnetic field strength (B) will decrease by a factor of four.<br /><br />Therefore, the density of the flux lines will **decrease** by four times.<br />