Electric Field Lines
Place charges in space and watch electric field lines form in real time. Understand superposition and field behavior visually.
Key Notes
Electric field (E) at a point is the force experienced by a unit positive test charge placed there: E = F/q₀.
Coulomb's Law: F = kq₁q₂/r², where k = 9 × 10⁹ N·m²/C² = 1/(4πε₀).
Field lines originate from positive charges and terminate on negative charges. They never cross.
The density of field lines indicates field strength — closer lines mean stronger field.
Electric field due to a point charge: E = kq/r², directed radially outward for +q, inward for −q.
Superposition principle: The net field at a point is the vector sum of fields due to individual charges.
In a uniform field, field lines are parallel and equally spaced.
At the surface of a conductor, the electric field is always perpendicular to the surface.
Formulas
Coulomb's Law
Force between two point charges.
Electric Field (point charge)
Field magnitude at distance r from charge q.
Field Due to Dipole (axial)
On the axis of a dipole, far from it.
Field Due to Dipole (equatorial)
On the perpendicular bisector of a dipole.
Dipole Moment
Product of charge and separation distance.
Force on Charge in Field
Force on charge q in electric field E.
Important Points
Electric field inside a conductor in electrostatic equilibrium is ZERO.
Field lines are perpendicular to equipotential surfaces.
A dipole in a uniform field experiences torque τ = pE sinθ but zero net force.
A dipole in a non-uniform field experiences both torque and a net force.
The number of field lines from a charge is proportional to the magnitude of the charge.
In JEE, superposition + symmetry arguments simplify complex charge distribution problems.
Electric Field Lines notes from sciphylab (also known as SciPhy, SciPhy Lab, SciPhy Labs, Physics Lab). Class 12 physics revision for JEE Mains, JEE Advanced, NEET UG, AP Physics 1/2/C, SAT, and CUET-UG.