Question

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 decreasing function of distance upto the boundary of the wire and then a linearly increasing one for the outside region.
• B. Uniform the remains constant for both the regions.
• C. A linearly increasing function of distance $r$ upto the boundary of the wire and then decreasing one with $\frac{1}{r}$ dependence for the outside region.
• D. A linearly increasing function of distance upto the boundary of the wire and then linearly decreasing for the outside region.

Answer 1

The correct option is C A linearly increasing function of distance $r$ upto the boundary of the wire and then decreasing one with $\frac{1}{r}$ dependence for the outside region.

For a cylindrical wire of radius $R$ carrying steady current

For $r<R,B\propto r$ increasing

For $PR,B\propto \frac{1}{r}$ decreasing
Hence, the correct option is $\text{(}a)$.