일반물리학 2 — Current and Resistance: Problem 41

41 A fuse in an electric circuit is a wire that is designed to melt, and thereby open the circuit, if the current exceeds a predetermined value. Suppose that the material to be used in a fuse melts when the current density rises to 440 A/cm². What radius of cylindrical wire should be used to make a fuse that will limit the current to 6.0 A?