From Ampere's circuital law for a long straight wire of circular cross-section carrying a steady current,the variation of magnetic field in the inside and outside region of the wire is :

• A
  a linearly increasing function of distance up to the boundary of the wire and then linearly decreasing for the outside region.
• B
  a linearly increasing function of distance $r$ up to the boundary of the wire and then decreasing one with $1/r$ dependence for the outside region.
• C
  a linearly decreasing function of distance up to the boundary of the wire and then a linearly increasing one for the outside region.
• D
  uniform and remains constant for both the regions.