# Consider a closed loop C in a magnetic field as shown in the fig. The flex passing through the loop is defined by choosing a surface whose edge coincides with the loop and using the formula $\phi = B_1 . dA_1 + B_2 . dA_2 + ...........$ Now if we choose two different surfaces $S_1$ and $S_2$ having C as their edge, would we get the same answer for flex. Justify.
(a) No, they will not be the same as the no. of magnetic lines passing through $S_1$ is not equal to the no. of magnetic lines passing through $S_2$
(b) Yes, they will be the same, as the no. of magnetic lines passing through $S_1$, is equal to the no. of magnetic lines passing through $S_2$
(c) It cannot be determined because the no of magnetic lines might or might not vary in $S_1 and S_2$