Electric Field Lines
A line drawn in electric field such that tangent to the line at point on it gives the direction of electric field at that point, is called electric field line.
(i) Electric field lines emerge form a positive charge and terminate into a negative charge.i.e.Electric lines of force usually start or diverge out form positive charge and end or converge on negative charge.
So, near an isolated positive charge, the electric lines of force are directed radially outward, while near an isolated negative charge, the electric lines of force are directed radially inwards.
(ii) Tangent to the field line at any point gives the direction of field at that point.
(iii) Electric lines of force never cross each other.(Because at the point of intersection there will be two different directions of net electric field, which is impossible)
(iv) The density of field lines is proportional to the strength of the field.
(v) Electric( Electrostatic) field lines never form closed loops.
(vi) Electric field lines do not exist inside a conductor.
(vii) Electric field lines are always perpendicular to the surface of a charged or uncharged conductor(equipotential surface).If a line of force is not normal to the surface of a conductor, electric intensity will have a component along the surface of the conductor and hence conductor will not remain equipotential which is not possible as in electrostatics conductor is an equipotential surface.
(vii) In a uniform electric field, the electric lines of force are equidistant, parallel straight lines.If the lines of force are equidistant straight lines the field is uniform and if lines of force are not equidistant or straight lines or both, the field will be non-uniform. The first three represent nonuniform field while last shows uniform field.
(ix) If a metallic solid sphere is placed in a uniform electric field, then the lines of force are normal to the surface at every point but they cannot pass through the conductor.
(x) The electric field lines move away from each other as they enter into a non conducting (dielectric) material.
Example:
Electric Field lines for a pair of identical charged particles kept at a separation.
Example:
Electric Field lines for an electric dipole.
Example:
Electric Field lines for a positive point charge kept in front a plane conducting sheet.
Example:
Two charged conducting (metal) sheets kept parallel to one another.
Question. A Solid metallic sphere is placed in a uniform electric field. Which of the lines A, B, C and D shows the correct path and why ?
Ans: Path (D), this is because ,
(i) there should not be any field line inside the conductor.
(ii) The field line must be perpendicular to the surface of conductor.
