The magnetic field 35.0 cm away from a long, straight wire carrying current 3.00 A is 2.00 µT
(a) At what distance is it 0.200 µT?
(b) At one instant, the two conductors in a long household extension cord carry equal 3.00-A currents in opposite directions. The two wires are 3.00 mm apart. Find the magnetic field 35.0 cm away from the middle of the straight cord, in the plane of the two wires.
(c) At what distance is it one-tenth as large? You will need to do a little algebra to get this result. Try to work out a general equation for the magnetic field as a function of r and d (the separation between the wires).
(d) The center wire in a coaxial cable carries current 3.00 A in one direction, and the sheath around it carries current 3.00 A in the opposite direction. What magnetic field does the cable create at points outside the cables?