Physics - Magnetism Question with Solution | TestHub

The direction of $\mathrm{dB}$ is the direction of vector $\mathrm{dl}\times \mathrm{r}$. From right hand screw rule, if we place a right handed screw at the point where the magnetic field is needed to be determined and turn its handle from dl to $\mathrm{r}$, then the direction in which the screw advances gives the direction of field $\mathrm{dB}.$