Refractive index

You must have seen that an object like pen bends in water! Do you know why? Let us discuss:

Every object has refractive index. Oh, do you know what is refractive index (n). It is the ratio of the speed of light in air (c) to speed of light in medium (v), that is

n = c/v

Origin of the term refractive index: Refractive comes from the word refraction that is “bending” and index from “point out” or “refer”. Thus refractive index signifies that how much light bends in a medium.

More the value of it, it means more the light bends in that medium.

For example, water has refractive index 1.33 and air has approximately 1. It means the light will bend more in water than air. Therefore the objects in water appears bended.

Glass has approximately 1.7 refractive index, so light will bend more in glass as compare to water.

Value of n can not be lesser than 1. Can you tell the answer, if yes, then please share your answer in the comment section.

Principle and parts of an optical fiber

Fibre optics: The term fiber optics originated from “fiber- thread like structure” and “optics-light”. It means a thread like structure through which light will pass.

Principle: The principle of optical fiber is “total internal reflection”.

Do you know what is total internal reflection: In this phenomenon, light should pass from denser to rarer medium and angle of incidence should be more than the critical angle.

Then the question arises what should be rarer and denser medium in optical fibers?

Let us discuss the parts of a fiber:

An optical fiber has following parts:

1. Core- It is the innermost part of the fiber.

2. Clad- It is outer part of the fiber.

3. Jacket or Sheath- It is the outermost part of an optical fiber.

Figure: Fiber parts

Core acts as denser medium and cladding as rarer. Thus, light passes through the core after total internal reflection.

Another purpose of clad is to provide mechanical strength to the core.

The function of the sheath is to protect the fiber from external impurities or contaminants.

Equation of continuity


Statement: Equation of continuity represents the law of conservation of charge. That is the charge flowing out (i.e. current) through a closed surface in some volume is equal to the rate of decrease of charge  within the volume :

I = -dq/dt                     (1)

where I is current flowing out through a closed surface in a volume and

-dq/dt is the rate of decrease of charge within the volume.

As  I = ∫J.ds and q = ∫ρdv

Where J is the Conduction current density and  ρ is the Volume charge density

Substitute the value of I and q in equation (1), it will become

∫J.ds = -∫dρ/dt dv       (2)

Apply Gauss’s Divergence Theorem to L.H.S. of above equation to change

surface integral to volume integral,

∫[divergence (J)]dV = -∫(dρ/dt) dv

As two volume integrals are equal only if their  integrands are equal

divergence (J) = – dρ/dt

This is equation of continuity for time varying fields.

Equation of Continuity for Steady Currents: Continue reading “Equation of continuity”

How to write research paper?

To write a research paper is not a simple thing but at the same time it is also not a difficult process. But it is certainly different from writing of an ordinary letter. When I have authored my first research paper, it was rejected twice. Then with the grace of almighty and blessings of my angel, my first paper accepted in a reputed journal of Elsevier. Therefore, let us see what exactly require to write a research paper:

1. Title: First thing is to write the title of the paper. It should be small but at the same time reflects your work.

For example: Influence of ———————————————-

2. Authors’ Name: All the names of the researchers should be mentioned. There will be one corresponding author with whom the journal editorial office will do all the correspondence.

example: Amita, Johnb

a institute name, binstitute name

3. Affiliation Name: The name of the institute should be mentioned below the name of the authors. See the above example.

4. Abstract: Abstract means the summary of your research. Abstract must include your work and important results of the work. It is not necessary to include that how the work is done?

5. Introduction: Introduction includes the literature review and why the work is done or how you reach the work to be done? Therefore, it is one of the most important part of the research paper. Literature review must be done with proper references. There are different styles to mention reference in text. One of the common way is to mention the reference at the end of the cited paper. For example: Knothe has studied the dependence of stability on fatty acid [1]. [1] means it will be mentioned first in the reference list. Another method is to add reference as superscript. For example: Knothe has studied the dependence of stability on fatty acid.1 Thus, the style can vary from journal to journal. Continue reading “How to write research paper?”

Probable interview questions and answers

The following article is contributed by my student Ms. Shivani Bhan.  She is  presently working in Tech Mahindra. I hope it will be beneficial for the students:

Its been 4 years now since I have been working – during this period I have working in 2 companies however I have given more that 15 interviews, not because I wanted to change, but because I wanted to know where the market is going and what they are seeking in a “Business Analyst”. This not only gave me confidence but also let me know some new things that were there in the market and I was unaware of the same coz my present company did not work on it. So its important to keep exploring the market. Discuss your profile, what you do, how you do etc with someone more experienced and seek their advice, learn from their experiences.

I always used to read the JD carefully and then reframe my resume as per same – not exactly – but yes somewhat similar as per the JD. Then I used to read a lot and explore the new topics – so that I am not blank in the interview room – its always better to say u have little knowledge – rather than saying you have not knowledge. Always do ur homework – as in be prepared with all sort of questions that can be asked. Continue reading “Probable interview questions and answers”