The figure shows the cross section of two long coaxial tubes carrying equal current `I` in opposites directions. If `B_1` and `B_2` are magnetic fields at point 1 and 2 as shown in figure then

Options

A. `B_1!=0,B_2=0`
B. `B_1=0, B_2=0`
C. `B_1!=0,B_2!=0`
D. `B_1=0, B_2!=0`

Answer

A

Explanation

At distance `r` from centre,
`B=mu_0/(2pi) (i_("in"))/r` (From Ampere's circuital law)
For path -1, `i_("in")=!0`
`:. B_1!=0`
for path -2 `i_("in")=0`
`:. B_2=0`