JEE Main202529 Jan 2025Morning ShiftPhysicsMagnetic Effects of CurrentActual
Consider a long straight wire of a circular cross-section (radius a) carrying a steady current I. The current is uniformly distributed across this cross-section. The distances from the centre of the wire's cross-section at which the magnetic field [inside the wire, outside the wire] is half of the maximum possible magnetic field, any where due to the wire, will be
Options
- A([a / 4,3 a / 2] )
- B([a / 4,2 a] )
- C([ a / 2,2 a ] )
- D([a / 2,3 a] )
Correct answer
C. ([ a / 2,2 a ] )
Step-by-step solution
Maximum possible magnetic field is at the surface aligned & B _ = ₀ I 2 a & ~B _ 2 = ₀ I 4 a aligned It can be obtained inside as well as outside the wire For inside, aligned & ₀ I 4 a = ₀ Ir 2 a ^2 & r = a 2 aligned For outside aligned & ₀ I 4 a = ₀ I 2 r & r =2 a aligned Correct answer [ a 2 , 2 a ]