Electrostatics is a vital branch of Physics. It is an interesting branch and questions
are often asked from it in the JEE. It is important to have a strong grip on the
topics of electrostatics in order to remain competitive in the JEE.
Electrostatics is the branch of Physics which is concerned with the study of those
electric charges which are at rest or are stationary. It goes way beyond the study
and exploration of the various properties of electricity and its applications. We
illustrate this concept with the help of an example. When a rod of plastic is rubbed
with fur or a glass rod is rubbed against silk, then it is generally observed that
the rods start attracting some pieces of paper and seem to be electrically charged.
While the charge on plastic is defined to be negative, that on silk is considered
positive. The vast amount of charge in an everyday object is usually hidden, comprising
equal amount of two kinds – positive and negative. The imbalance is always small
compared to the total amounts of positive charge and negative charge contained in
Electrostatics involves the building up of charge on the surface of the objects
as a result of contact with other surfaces. The charge exchange occurs only when
two surfaces come in contact and then finally separate. The effects as a result
of this exchange can be noticed only when at least one of the two surfaces who came
in contact is highly resistive to the electrical flow. The reason behind this is
that these kinds of charges which are transmitted to or from highly resistive surface
remain trapped there for a sufficient duration so that their effects can be observed.
These charges stay there and ultimately they either ooze out in the form of bleeding
to the ground or need to be immediately neutralized by a discharge.
The electromagnetic forces are vital forces which interact with particles in a
variety of ways and this includes the minimal reactions of electrostatics.
Types of charges and their nature….
We have already discussed that there are two types of charges- positive and negative.
It is a fundamental fact that while like charges repel, the unlike charges attract
each other. This law forms the base of electrostatics. If two unlike charges are
brought close to one another, they are pulled towards each other whereas if two
like charges are brought close they are pulled away from each other.
We discuss some of the characteristic features of an electrically charged
Firstly, the law which has already been discussed applies i.e. like charges repel
and unlike charges attract. Main point to be note here is that the charge is conserved.
As discussed in the earlier example of rod and fur, the net negative charge on the
rod is same as the net positive charge on the fur.
View this video for more on electrostatics
Concepts of conductor and insulator...
As the name suggests, a conductor is the material which conducts electric charges
or through which the charges can easily pass. Contrary to this is the concept of
insulators. Insulators do not allow electric charges to pass through them easily.
The charges on a conductor always assemble at the sharp points as a result of properties
of electric fields. Let us consider the example of a metal cone. Obviously, due
to the result explained just now, the charged cone will have maximum charge on its
sharp edge and less charge elsewhere.
1. Human body acts like a conductor and lets current to easily flow through it.
It is for this reason that one should be careful with the useful of electrical appliances.
2. Each type of material has a different arrangement of atoms, electrons and protons.
This arrangement makes it a conductor or an insulator.
3. Metals are considered to be very good conductors while rubber is an insulator
as it does not allow electric current to pass through it easily.
4. We list some of the items which are considered to be positively charged:
· Human hair
Applications of Electrostatics
Electrostatics deals with electromagnets and is used in numerous fields. Its major
application is in paint spraying. Other uses include: