Two identical current-carrying coaxial loops, carry current I in an opposite sense. A simple amperian loop passes through both of them once. Calling the loop as C,

a. B.dl=2μ0I.
b. the value of B.dl is independent of the sense of C.
c. there may be a point on C where B and dl are perpendicular.
d. B vanishes everywhere on C.

Which of the above statements are correct?
1. a and b
2. a and c
3. b and c
4. c and d

(3) Hint: The magnetic field depends on the current.
Step 1: Applying the Ampere's circuital law, we have,
cB.dl=μ0(II)=0 (because the current is in the opposite sense.)
Step 2: Also, there may be a point on C where B and dl are perpendicular and hence;
cB.dl=0