A long curved conductor carries a current I (I is a vector). A small current element of length \(\mathbf{d} l\), on the wire induces a magnetic field at a point, away from the current element. If the position vector between the current element and the point is \(\mathbf{r}\), making an angle with current element then, the induced magnetic field density; \(\mathbf{d B}\) (vector) at the point is ( \(\mu_0=\) permeability of free space)

1. A \(\frac{\mu_0 \mathbf{I d} l \times \mathbf{r}}{4 \pi r}\) (perpendicular to the current element \(\mathbf{d} l\) )
2. B \(\frac{\mu_0 \mathbf{I} \times \mathbf{r} \times \mathbf{d} l}{4 \pi r^2}\) (perpendicular to the current element \(\mathbf{d} l\) )
3. C \(\frac{\mu_0 \mathbf{I} \times \mathbf{d} l}{r}\) (perpendicular to the plane containing the current element and position vector \(\mathbf{r}\) )
4. D \(\frac{\mu_0 \mathbf{I} \times \mathbf{d} l}{4 \pi r^2}\) (perpendicular to the plane containing current element and position vector \(\mathbf{r}\) )