Spectroscopy

 Spectroscopy was born with the discovery of presence of seven distinct color in white light. Splitting of white light gave birth to thoughts of study of variation of light and its various wavelengths under various situations. Initially due to lack of advance apparatus only visible light was used for spectroscopy. However with the development of advance instruments it became possible to use other part of spectrum (like infra red and ultra violet light) for purpose of spectroscopy. Spectroscopy results are constructed due to difference of intensity at different points.

Image showing spectrum of light indicating start of field of spectroscopy

Spectroscopy is a technique that uses spectrum of radiations to reveal information about different structure. These structures may be a tissue or cell or an atom or a molecule. Spectroscopy uses instruments that produce radiations and detect theses radiation after their interaction with above mentioned structures. There is difference in spectra before and after interaction and this difference makes the basis of spectroscopy. Spectroscopy has been used for quite some time for medical purposes. Continuous development in the field of spectroscopy has lead to development of modern sophisticated techniques that are in use today. Different types of spectroscopy techniques are listed below:

1. Infrared spectroscopy : Uses Radiations having wavelengths in infrared radiation.

2. Nuclear Magnetic resonance spectroscopy: makes use of nucleus and magnetic field interaction

3. Ultraviolet spectroscopy: Uses radiations in ultraviolet region of light

4. Electronic absorption spectroscopy: Involves excitation and de-excitation of electrons

5. Electronic luminescence spectroscopy: deals with emission from transition between electronic states

6. Spectroscopy using optical activity of chiral media: Chiral media behaves differently for left and right polarized light

7. Vibrational Spectroscopy: make use of atomic vibrational modes

8. Fluorescence correlation spectroscopy: Fluorescence correlation spectroscopy measures the correlation between fluorescence intensities at two different times

As mentioned earlier these techniques of spectroscopy make use of fact that radiations have different spectra of emission and absorption while interacting with tissues. Spectrum is a graph or plot of radiation intensity with respect to wavelength or frequency. Apparatus used for this purpose of spectroscopy is known as spectrograph. These different types have been developed to deal different scenarios and challenges posed by diversity of objects to be studied. 

You may have an impression from every day life applications of these radiations that spectroscopy is something that is only useful in medical field but this is not the case. Spectroscopy is equally important in other fields like physics and chemistry. So it can be said that spectroscopy is useful at greatly large scale having applications in astronomy and at very small scale having applications in atomic and molecular structure determination.

Although it has been around scientific world for years but spectroscopy is still an active stream of research for scientists and radiologists and many problems are under extensive study to develop, improve and enhance existing methodologies and technologies and reveal more information that is still not available to us for better understanding of natural phenomena. 

 

Why does ice float on water surface?

 watch video description here.

Why does ice float on water surface? Why does ice not sink into water? Reason for ice floating on water surface. Explanation for ice floating on water surface.

All of you must have seen an ice cube floating on water surface. It is a daily life observation that when an ice cube is placed in a glass of water it starts floating on water surface instead of sinking into it. This observation is a common scientific question for students of science. It is very easy to understand in terms of density of water and ice. Ice floats on water surface due to its lower density compared to water. 

watch video description here.

Diffraction and Crystal Structure

Diffraction is usually considered to be a phenomenon associated with waves. Waves are known to have properties of reflection, refraction, interference and diffraction. Diffraction of waves is defined by bending of waves around an obstacle present in path of waves. A famous experiment known as Young's double slit experiment is considered to be the first instance that made diffraction prominent in the study of waves.

Schematic of double slit experiment for study of diffraction

 After observing the interference pattern obtained due to diffraction of light, diffraction have of waves have been used in many applications. Many devices or instruments have been developed that are used to study diffraction. Most widely used application of waves diffraction is to determine crystal structure with the help of X-rays. Inter atomic and inter planar space in crystals is almost of same size as that of wave length of X-rays. As condition for diffraction is that wave length of waves should be comparable to the size of slit which in case of crystals is inter atomic space so X rays are good candidate to study crystal structure via diffraction. This study of crystal structure is governed by Bragg's law. Bragg is the name of scientist who first successfully explained the diffraction of waves from crystal. If we know wave length of incident wave and glancing angle (Angle with which a wave is incident on crystal), then we can easily determine inter planar spacing. Instrument used for determining crystal structure with the help of Bragg's law is known as Bragg's spectrometer. Bragg's spectrometer measures the intensities of waves after passing through crystals and determine whether these waves are interfering constructively or destructively. When diffracted interfering waves interfere constructively, a bright spot is observed and when these interfere destructively a dark spot is observed. There are other methods also available that make use of diffraction for structure determination of crystals. These methods include powder method, electron diffraction, neutron diffraction, Laue's method etc. Mentioning of electron and neutron diffraction must be shocking to some readers but this is another reason that make diffraction an ever green phenomenon to be explored and studied. Louis de Broglie, in 1924, suggested that matter has dual nature. This means that matter can also behave as wave under certain conditions. By using momentum and Planck's constant , one can easily determine wave length of wave associated with a particle. This wavelength is equal to the ratio of Planck's constant and momentum of particle. This wavelength for massive objects is very small and can not be detected with present day equipment however for small particles like electrons and neutron it has appreciable wavelength and can be measured and observed. This wave nature of particles has now been verified and is also being used for studying crystal structure. Wave nature of electrons was also verified by using double slit experiment. Presence of interference pattern on observation screen proved that electrons behaved as waves and produced interference pattern due to diffraction from slits. Sill large scale research is being carried out for the improvement of experimental setups involved in crystal structure studies. In schools and colleges an instrument named diffraction grating is used for the demonstration of diffraction of light. Here you can see diffraction, its physical significance, and application in a small video. click to watch. 

If you are curious enough to observe interference by yourself, then the good news is that you can do it with great ease at your home and all you need is a torch and solid sphere ( a tennis ball ). Get inside a room, turn off lights, turn your torch on and point towards the wall. Now place the ball in the path of torch light. You will observe a bright spot at the center of shadow of ball. The bright spot in due to diffraction (bending of light around obstacle). If diffraction had not occurred , we would not be able to observe dark spot. Do this fun activity and share your results with us about diffraction of light in comment section.