Field line geometry and charge configuration
Electric field lines emanate radially outward from positive charges and converge inward to negative charges. The density of field lines at any location represents the field strength: closely spaced lines indicate a strong field, while sparse lines indicate a weak one. This visual representation transforms abstract field concepts into concrete geometry. A single point charge produces radial field lines in all directions. Two opposite charges produce lines that leave the positive charge and terminate at the negative charge, with field strength varying inversely with distance squared. Multiple charges create complex patterns where field lines never cross, revealing the superposition principle at work.
Magnetic field circulation around current sources
Magnetic field lines form closed loops around current-carrying wires, unlike electric field lines which originate and terminate on charges. A straight wire produces concentric circular field lines when viewed end-on, demonstrating that magnetic fields have no sources or sinks comparable to electric charges. The direction of circulation (clockwise or counterclockwise) depends on the current direction, following the right-hand rule. Current loops produce field patterns that resemble bar magnets, establishing the connection between electricity and magnetism. This circulation property of magnetic fields underlies all electromagnetic induction: changing magnetic flux through a loop induces an electric field that drives current, the principle underlying generators and transformers.