Right-hand screw rule

Corkscrew driven by right hand downward into the cork.

The right-hand screw rule, also known as corkscrew rule, associates the direction of an electric current with the direction of the magnetic force lines circling the current, see Ampère's law.

The corkscrew rule is depicted in the photograph, where the corkscrew is rotated downward into the cork. When the electric current runs straight downward through the center of the corkscrew, the magnetic force lines are directed along the green line shown in the photograph.