1
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
- Uniform and remains constant for both the regions.
- A linearly increasing function of distance upto the boundary of the wire and then linearly decreasing for the outside region.
- A linearly increasing function of distance r upto the boundary of the wire and then decreasing one with 1r dependence for the outside region.
- A linearly decreasing function of distance upto the boundary of the wire and then a linearly increasing one of the outside region.
Answer
(3) A linearly increasing function of distance r upto the boundary of the wire and then decreasing one with 1r dependence for the outside region.
Solution
Let the wire of radius a carry current I uniformly over its cross-section.
Inside (r < a): current enclosed Ienc = I r2a2
B(2 r) = 0 I r2a2
B = 0 I r2 a2 r (increases linearly)
Outside (r > a): B(2 r) = 0 I
B = 0 I2 r 1r
B increases linearly up to the surface and then decreases as 1r outside.
Answer: (3)
NEET (UG) 2022