When a glass rod is rubbed with silk, the rod acquires one kind of charge while the silk
acquires the second kind of charge. This is true for any pair of objects that are rubbed to get
them electrified. Now if the electrified glass rod is put in contact with silk, (with which it was
rubbed), the two no longer attract each other. They also do not attract or repel other light
objects as they did on being electrified.
Thus, the charges acquired after rubbing are lost when the charge bodies are brought in
contact. What can one conclude from these observations?
4. INTRODUCTION
It is a matter of common experience to see a tiny spark, or hear a crackle, when one takes off
synthetic clothes or sweaters, particularly in dry weather. Have you ever tried to find any
explanation for this phenomenon? Another common example of electric discharge is the
lightening that we see in the sky during thunderstorms. We may also experience a sensation
of a mild electric shock either while opening the door of a car or holding the iron bar of a bus
after sliding from our seat. The reason for all such experiences is the discharge of electric
charges through our body, which were accumulated due to rubbing of insulating surfaces.
You might have also heard that this is due to generation of static electricity. This is precisely
the topic we are going to discuss in this unit.
Static means anything that does not move. Electrostatics deals with the study of forces, fields
and potentials associated with static charges.