The simplest current we can come up with is a current flowing in a straight line, such as along a long straight wire. The magnetic field from a such current-carrying wire actually wraps around the wire in circular loops, decreasing in magnitude with increasing distance from the wire. To find the direction of the field, you can use your right hand. If you curl your fingers, and point your thumb in the direction of the current, your fingers will point in the direction of the field. The magnitude of the field at a distance r from a wire carrying a current I is given by:

 Right-Hand Rule determines the direction of the magnetic field around a current-carrying wire and vice verse 

 Using your right-hand: 

Curl your fingers into a half-circle around the wire, they point in the direction of the magnetic field, B


Point your thumb in the direction of the conventional current.