Electrostatic induction is the separation of electric charges on a neutral conductor when it is placed close to but not touching a charged body. Figure below shows a neutral conductor placed besides a positively charged glass rod.

Free electrons in the neutral conductor are pulled towards the positively charged rod. The side of the conductor beside the rod acquires a net negative charge while the other side acquires a net positive charge.

The charges that appear on the neutral conductor are called induced charges; these charges are equal and opposite. The induced charges will disappear if the charged rod is taken away.

Attraction of uncharged objects

         Charged materials can also attract uncharged objects. The figure above can be used to explain how this is possible. The attraction between the negative (near) side of the conductor and the rod is stronger than the repulsion between the

Positive side and the rod; the resultant force is attractive.

Insulators do not contain free mobile electrons. However, if an insulator is placed beside a charged object, slight displacements of the electrons in the insulator can cause the induction of charges in the insulator.

A comb rubbed in dry hair can pick up tiny dust particles, tiny pieces of paper, etc.

Similarly, a balloon rubbed with a dry cloth can stick on a wall. The balloon or the comb becomes charged when rubbed in dry hair or dry cloth respectively and is attracted to uncharged objects because of the charge induced in the uncharged objects.

                 Earthing or grounding

Earthing a material means making it to become neutral or uncharged by creating a contact between it and the earth.

 The earth has excess amount electric charges; positive and negative.

 Figure above shows discharging by earthing

• If a negatively charged conductor is earthed, it loses the excess electrons to the earth and becomes neutral.
• Likewise if a positively charged conductor is earthed, electrons flow from the earth to neutralize the excess positive charges so that it becomes neutral. This is shown in the figure above.

Note that a charged insulator cannot be discharged by earthing because electrons do not move freely in it.

A Conductor can be earthed by touching it with a finger because we are poor conductors, so the charges will leak through the body to the earth.