Q. Movement of principal ray?
In every case a principal ray moves from the head of the object to the plane of the lens. It passes through the plane of the lens as well as continues travelling into the space on the other side of the plane of the lens the side opposite that on which the object resides. In depicting principal rays one should include at least one arrowhead pointing toward the plane of the lens on the ray segment that extends from the head of the object to the plane of the lens as well as at least one arrowhead pointing away from the plane of the lens on the ray segment on the other side of the lens the side opposite that on which the object resides.