Right-hand thumb rule: if the thumb of the right hand points along the direction of current in a straight wire, the curled fingers indicate the:

1. Grip the wire with the right hand, thumb pointing along the current. 2. The curled fingers give the direction of the magnetic field LINES around the wire. 3. Hence concentric circles of B field around a straight current-carrying conductor. _Source: NCERT Class 10 Science Ch 12 §12.2 Magnetic Field by Current_