What is resistance and reason for it?

You must have knowledge of current. As current is the charge per unit time.
Resistance is the obstruction offered to the flow of current.
Reason: As charge (electrons) flow through the wire (conductor), electrons collide with the walls of the conductor and they also collide with each other. Due to this collision, obstruction occurs and this is called resistance.
Let us understand the concept of resistance with a common daily life experience:
Suppose, you are walking at a place where there is no person, it means you are free to move. Now suppose you are moving at delhi or mumbai railway station, then what will happen? You will face lots of people and you will now face obstruction for your movements. This is basically resistance.

IAS preliminary exam new pattern

Many of us want to appear in the prestigious exam and one of the most difficult exam called “civil services”.
Let us discuss about it:
To clear civil services, one has to pass to three steps:
a) Preliminary exam
b) Main exam (for candidates who clear preliminary exam)
c) Interview (for candidates who clear main exam).

Today I will discuss about the preliminary exam only:
From 2011, the pattern and syllabus of preliminary exam of civil services is going to be changed.
The Preliminary Examination  will consist of two papers of objective type carrying a maximum of 200 marks for each paper.
Paper 1 Continue reading “IAS preliminary exam new pattern”

Non polar dielectrics

In the last article, I have discussed the dielectrics and polar dielectrics. Today let us discuss the non-polar dielectrics:

Non-polar Dielectrics or Molecules.  If  the  centre of gravity of  positive charges  coincides  with the centre of gravity of negative charges then the dielectric is called non-polar dielectric.

Example. H2, N2 etc.

Thus, a non-polar dielectric has a zero electric dipole moment In the presence of electric field, the charge centres get displaced and dielectric or molecule is then said to be polarized and therefore dielectric  acquire an induced dipole moment in the direction of the field.

Note : After reading this article, you will be able to answer the following questions:

What are  non-polar dielectrics,

What are non-  polar molecules,

Write the examples of non-polar dielectric materials,

Why  non-polar molecules have zero dipole moment

Dielectrics and their types


Dielectrics are the materials which do not contain free charges for conduction.

Thus, dielectrics are basically insulators as insulators do not conduct electricity through them. But, dielectrics, contain positive and negative charges which are bounded  together and these charges could be effected by
the electric field. The main function of dielectric is the charge storage.


An atom contains a  positive charge  in the nucleus and negative  charge (electrons) orbitting around the nucleus. The positive as well as the negative charges can be considered to be concentrated at a point. The point  at which the positive  charge can be assumed to be concentrated is termed as the centre of  gravity of the positive charge. Similarly, the point at which the negative charge can be assumed to be concentrated is termed as the centre of gravity of the negative charge. Now we can define the polar and non-polar dielectrics as :

Polar Dielectrics or Molecules: Continue reading “Dielectrics and their types”

Electric Field Intensity Due To A Point Charge

Electric Field Intensity Due To A Point Charge

Suppose we have to calculate electric field intensity at any point P due to a point charge q at O, where OP= r.

Consider a small positive test charge q0> at P.

According to Coulomb’s law, force at P is

F = 1/4Пεo qq0/r2 ar

where ar is unit vector directed from q towards q0.

As                    E = F/q0

Therefore by putting value of F in above equation, we get

E =       1/4Пεo q/r2 ar Continue reading “Electric Field Intensity Due To A Point Charge”



It is defined at any point as the force experienced by unit positive charge placed at that point.

The electric field intensity at any point is the strength of electric field at that point.

If F  is the force acting on a test charge + q0 at any point, then electric field intensity at this point is given by

E = F/q0

Electric field intensity is a vector. The direction of E is the same as the direction of F that is E is along the direction in which the test charge  + q0 would tend to move.

The S.I. unit of electric field intensity is newton per coulomb.

Physical Significance Continue reading “ELECTRIC FIELD INTENSITY”

Retired but not yet tired

The writer is a retired Major General …not retired from life..just retired from his post.

Currently employed with TATA’s as an Advisor and also writes for various magazines mainly on the national security .

1.      Retirement from service in our society is a rather recent phenomenon. It was possibly started by the British. In a nation where people want to be paid without doing their assigned jobs, a paid permanent sabbatical on reaching the age of superannuation is an icing on the cake.

2.      Superannuation is an acknowledgement by the system that the concerned person has spent his or her productive years in the service of the organization and should make way at a certain age for others to move up the ladder. It is hoped that by this time the person concerned would have taken care of all his obligations, collected enough money to look after his needs and would be looking forward to a well-deserved break from the routine. Continue reading “Retired but not yet tired”

Coulomb’s law and its limitations


Statement. The force of interaction between two stationary point charges q1 and q2 is directly proportional to the product of the charges and inversely proportional to the square of the distance r between them.

That is,

F α q1q2/r2

If the charges are placed in vacuum, then

F = 1/4Пεo q1q2/r2

where 1/4Пεo is a proportionality constant.

εo is the permittivity of free space = 8.85418 x 10-12 C2 /Nm2 or Farad/m

Definition of coulomb: Continue reading “Coulomb’s law and its limitations”



There are three types of charge distributions :

a) Linear Charge Distribution. In this distribution the charge is distributed uniformly along a line in a straight line or circumference of a circle. This is represented by λ, the linear density of charge, which is equal to charge per unit length.

λ =dq/dl

Where dq is a small amount of charge in small length dl.

It is measured in C/m.

b) Surface Charge Distribution. Continue reading “CHARGE DISTRIBUTIONS”