Archive for June, 2011
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 More >
Name of the Institute: Shaheed Bhagat Singh College of Engineering & Technology is situated in the city Ferozepur (Punjab) of India.
Affiliated with: Punjab Technical University (PTU), Kapurthala
Approved by: All India Council for Technical Education (AICTE), New Delhi.
Courses offered: More >
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 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.
POLAR AND NON-POLAR DIELECTRICS
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: More >
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 More >
ELECTRIC FIELD INTENSITY
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 More >
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. More >
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.
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: More >
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.
Where dq is a small amount of charge in small length dl.
It is measured in C/m.
b) Surface Charge Distribution. More >