A constant direct current of uniform density `hatj` is flowing in an infinitely long cylindrical conductor.The conductor contains an infinitely long cylindrical cavity whose axis is parallel to that of the conductor and is a a distance `vecl` from it.What will be the magnetic induction `vecB` at a point inside the cavity at a distance `vecr` from the centre of cavity?

Options

A. `A. (mu_(0)(vecjxxvecr))/(2)`
B. `B. (mu_(0)(vecjxxvecl))/(2)`
C. `C. (mu_(0)(vecjxxvecl)+mu_(0)(vecjxxvecr))/(2)`
D. `D. (mu_(0)(vecjxxvecl)-mu_(0)(vecjxxvecr))/(2)`

Answer

B

Explanation

`B=mu_(0)/2[vecJxx(vecl+vecr)]+mu_(0)/2[-vecJxxvecr]`
`vecB=mu_(0)/2[vecJxxvecl]`