Cross and dot conventions, right hand thumb rule
CROSS AND DOT CONVENTIONS:- They represent the direction of current perpendicular to the two dimensional surface it has been represented upon (board, paper, screen etc.)
Perpendicular to the surface, there can be two possible directions a vector can take. It can either come out of the surface towards the observer and is denoted by the dot (.). Or it can go away from the observer into the surface, denoted by the cross (x).
RIGHT HAND THUMB RULE:- Right hand thumb rule was given by Maxwell. So this rule is also known as Maxwell’s right hand thumb rule. According to this rule, imagine that you are holding a current carrying wire in your right hand so that the thumb points in the direction of the current, then the direction in which the fingers wrap the wire will represent the direction of magnetic lines of force.