what is Electric lines of force

An Electric line of force is an imaginary straight or curved path along which a unit positive charge tends to move in an electric field.
The electric field due to simple arrangements of point charges are shown in below Fig
Isolated charge unlike charges like charges
the below Fig Lines of Forces
Properties of lines of forces:
(i) Lines of force start from positive charge and terminate at negative
charge.
(ii) Lines of force never intersect.
(iii) The tangent to a line of force at any point gives the direction of the electric field (E) at that point.
(iv) The number of lines per unit area, through a plane at right angles to the lines, is proportional to the magnitude of E. This means that, where the lines of force are close together, E is large and where they are far apart, E is small.
(v) Each unit positive charge gives rise to 1/ EO lines of force in free space. Hence, the number of lines of force originating from a point
charge q is N = q/EO in free space.
Electrostatic shielding, It is the process of isolating a certain region of space from external field. It is based on the fact that electric field inside a conductor is zero. During a thunder accompanied by lightning, it is safer to sit inside a bus than in open ground or under a tree.
The metal body of the bus provides electrostatic shielding, where the electric field is zero. During lightning, the electric discharge passes through the body of the bus. 1.5 Electrostatic induction It is possible to obtain charges without any contact with another charge. They are known as induced charges, and the phenomenon of producing induced charges is known as electrostatic induction. It is used in electrostatic machines like Van de Graff generator and capacitors. Fig 1.21 shows the steps involved in charging a metal sphere by induction. P/ R r1 O Gaussian  Surface Fig 1.20b Field at a point inside the shell 25 (a) There is an uncharged metallic sphere on an insulating stand. (b) When a negatively charged plastic rod is brought close to the sphere, the free electrons move away due to repulsion and start pilling up at the farther end. The near end becomes positively charged due to deficit of electrons. This process of charge distribution stops when the net force on the free electron inside the metal is zero (this process happens very fast). (c) When the sphere is grounded, the negative charge flows to the ground.
The positive charge at the near end remains held due to attractive forces. (d) When the sphere is removed from the ground, the positive charge continues to be held at the near end. (e) When the plastic rod is removed, the positive charge spreads uniformly over the sphere. 1.5.1 Capacitance of a conductor When a charge q is given to an isolated conductor, its potential will change. The change in potential depends on the size and shape of the conductor. The potential of a conductor changes by V, due to the charge q given to the conductor's α V or q = CV i.e. C = q/V Here, C is called as capacitance of the conductor. The capacitance of a conductor is defined as the ratio of the charge given to the conductor to the potential developed in the conductor.