Final answer:
Field lines illustrate the behavior of electric and magnetic fields, showing attraction and repulsion by the way they converge or diverge. Like poles repel and opposite poles attract, which is depicted by the density and the direction of the field lines. They also conform to the right-hand rule for representing forces on moving charges in magnetic fields.
Step-by-step explanation:
Magnetic and electric field lines are conceptual tools used to visualize and predict the behavior of magnetic and electric fields. If we consider magnetic field lines, the strength of the field is proportional to the closeness of the field lines - more precisely, it is proportional to the number of lines per unit area perpendicular to the lines.
When two like poles of a magnet (either two north poles or two south poles) are brought close together, they repel each other, causing the magnetic field lines to diverge. Conversely, when opposite poles are brought together, the field lines converge between the poles, indicating an attractive force. This can also be seen with electric charges, where field lines start on positive charges and end on negative charges. A dense number of lines indicates a strong field, which means that a positive test charge placed in this region would be strongly attracted or repelled depending on the nearby charge.
It must be noted that while field lines are useful for visualization, they are not physical entities. They provide a way to represent the direction and relative intensity of fields. Field lines for magnetic fields emanate from the north pole and end at the south pole of a magnet, or they may extend to infinity in theoretical cases. The direction of the lines follows the right-hand rule, which also aids in determining the force experienced by a moving charge in a magnetic field.