Line of force, it is particular line/ path followed by an electric charge it can be easily move in an electric field, else a mass free to move in an earth gravitational field, or generally any appropriate test particle in a given force field. The line force is always handled with the vector field, V = −grad ϕ, and also in addition a potential ϕ always travels normally to the equipotential region of surfaces, the changes in particular region of its traveling direction will be represented with the help of continuous lines drawn similar to that. The line & particular force acting on it is known as the line of force.
Next, the magnetic flux is known as the overall magnetic induction crossing a region of surface, equal to the integral of the component of magnetic induction, perpendicular to the region of surface over the region of surface. The magnetic flux through a region of surface is the region of surface integral of the normal component of the magnetic field B crosses through that region of surface. The SI unit of magnetic flux is the weber (Wb) and its CGS unit is the Maxwell. Magnetic flux is usually measured by the device named as the flux meter, which contains measuring coils and electronics that calculates the change in voltage in the measuring coils to evaluate the magnetic flux.