Reminiscing a dreadful day in my life. Today 16th April, a decade ago, 2007.
It was early morning. Snow flakes were making the surrounding really beautiful. Especially because I was sitting inside of a cozy air conditioned student center, looking out of the glass wall. The hazelnut flavored milk-less coffee used to be one of my favorite, especially when I would be sitting alone. I was reading a paper on “phenomenology of quantum mechanical phases related to my thesis research”. These were the days I had started writing or at-least musing about writing blogs. So I was even perhaps in the mood of writing a poem or something.
The beautiful silence was broken by a strange noise of a crowd. I looked around. A man with a long gun, as long perhaps as himself, of-course a bit smaller, wielding it to the ground was hailing at the folks around “stay indoor”. More…
Optics Series Lecture, Lecture – XIV, XV, XVI.
“Color of thin films, Newton’s rings, Lloyd’s mirror and Phase changes during reflection” These lecture were delivered on 16th February, 21st February and on 17th March. The lecture sessions were of 1 and 1/2 hours. The lectures were delivered to both Physics honors as well as Physics elective students on different days.
We have previously discussed what is interference and what is wave-front splitting and amplitude splitting interference. We have also discussed in much details two wave-front splitting interference viz. Young’s double slit interference (Lecture – IX) and Fresnel’s bi-prism (Lecture – XI). Today we will discuss one more wave-front splitting interference namely Lloyd’s mirror interference before moving onto the amplitude splitting interference of the Newton’s Rings. Also we will discuss two interesting and related concepts; i. Phase change on reflection and ii. Color of thin films. More…
If you have come across a daunting problem in MS word where a new blank page appears without your volition and you lose your mind cos you just can’t delete it, relax, the following will restore your peace if it already was available to you before MS misbehaved. We have covered your back. Sorry I copied the following magical solution from a comment section from the web after suffering silently the fool that “software helplessness” is. Yes, the following works like a charming mother in law. Thanks MILs. More…
Optics Series Lecture, Lecture – XI.
“Fresnel’s Bi-prism: measurement of wavelength of light by it.” This lecture was delivered on 16th February in a lecture session of 1 and 1/2 hours. This lecture was delivered to Physics elective students and later to honors students. This does not strictly pertain to 1 and 1/2 hours of regular lecturing session that we have mostly been employing. Thats because it was created with another part which can be optionally appended to other related subject matter. In the web-version thats what we will do. Our guiding principle is more in line with the honors course, where the subject matter is quite extensive and deep which brings more flexibility and choices into the lecture compositions.
Today we will discuss another interesting interference set-up, now that we have discussed the Young’s double slit experiment, in lecture – IX. A few words about the general mechanism behind interference. There are two kinds of interference basically that we will be discussing in our lectures. We discussed the Young’s DS interference pattern based on our understandings of intensity or irradiance patterns that we studied here: lecture – VII. Interference is sustained and visible if the corresponding sources of light are coherent among themselves, that is, if the sources have phase differences that are not arbitrarily or abruptly changing, as a consequence we can safely assume the phase differences are constant and therefore predictable. Incoherent light makes this impossible. Incoherent light is that light source whose production itself is arbitrary and abrupt and unpredictable, hence nothing can be definitively said on its phase, as a result the coherence is only short lived. If two light sources are so generated that their respective coherence time (or coherence length) are well within each others span, they are said to be coherent light. More…
“Electromagnetic Nature of Light — A brief history of light” This lecture was delivered on 16th March, yesterday, in a lecture session of 1 and 1/2 hours. The second part of this lecture was delivered to Physics honors as well as Physics elective students.
As I promised in the last lecture, lecture-X we have our one of the interesting historical and technical perspective about light that is also one of my favorite, as I discovered yesterday, or shortly before that, the night before, when I was composing the lecture from scratch. We will name this lecture with its proper number, only after its clear to us what chronological number it must be associated with it. Its like an advanced wave, it reached us before in time, before it was intended to be taken up for its web-version.
Let us begin this lecture which has roughly two parts, 1. the history of light and its understanding through the centuries and 2. the electromagnetic nature of light. The second part is intended as the course material for honors as well as elective students but you will be in amusement if you also cover the first part.
A brief history of light.
Various optical devices and optical phenomena have been known since close to 4000 years. The optical devices of ancient time includes mirrors, burning glasses, lenses and other magnifying devices.
Accordingly various properties and laws of light were understood and developed since these times. Eg light was understood to propagate rectilinearly, light was understood to reflect and refract. There were various laws that were known since these times which catered to the need for explanation of these phenomena. eg Reflection was understood to be a phenomena explained by the principle of shortest path — follow link to know this and other related ideas and their history: Hero of Alexandria. Laws of refraction were understood either partially or completely as the centuries or even millennia passed.
Apart from rectilinear propagation of light it was understood that light moves at infinitely large speed. Advanced optical devices such as telescopes were developed based on partial and faulty understanding of light which was gradually refined to accommodate better credits of advancement. More…
Optics Series Lecture, Lecture – X.
“Harmonic Spherical Waves” This lecture was delivered on 16th February in a lecture session of 1 and 1/2 hours. This lecture was delivered to Physics honors students.
In our lecture ( lecture-VIII ) we worked out the form of plane harmonic traveling waves. Note that soon we will barge into the concept of wave profile and how to convert a wave profile into its corresponding time-dependent or traveling form. But before we do that here is yet another general form of a traveling wave which we often meet in the Physicists Den. The traveling spherical wave fronts. Let us work out its details.
When a stone is dropped in water it sends out circular waves. Similarly a sphere or a glob of matter that oscillates inside of a water body would send out 3-dimensional waves or ripples. Sources of light wave, which we will study in great detail, in this course, to fulfill our insatiable hunger for understanding the nature of optical phenomena, similarly, send out oscillations which propagate radially and uniformly in all directions. These are the spherical waves and the points or region that move out with equal phase are the wave fronts in this case, spherical in shape, called as spherical wave fronts.
We evidently need to describe the spherical wave fronts in spherical polar coordinate system, owing to the spherical symmetry in problems of 3-dimensional propagation of light waves. More…