NEET2022PhysicsMagnetic Effects of CurrentActual
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
Options
- Aa linearly increasing function of distance upto the boundary of the wire and then linearly decreasing for the
- Ba linearly increasing function of distance r upto the boundary of the wire and then decreasing one with 1 r de
- Ca linearly decreasing function of distance upto the boundary of the wire and then a linearly increasing one fo
- Duniform and remains constant for both the regions.
Correct answer
B. a linearly increasing function of distance r upto the boundary of the wire and then decreasing one with 1 r de
Step-by-step solution
If the current density in the wire is J then For r < R ∮ B → · d l → = μ 0 i ⇒    B 2 π r = μ 0 J π r 2 ⇒    B = μ 0 J 2 r ⇒ B ∝ r For r > R ∮ B → · d l → = μ 0 i → ⇒   B 2 π r = μ 0 π R 2 J ⇒   B = μ 0 R 2 J 2 r ⇒ B ∝ 1 r