Fundamental Concepts in Applied Physics and Fluid Dynamics
Q.Explain the construction and working of Ruby laser with the help of energy level diagram
Ruby is a crystal of aluminum oxide Al2O3 in which chromium Cr3+ ions are added as impurity (0.5%).So its colour is pink. Ruby rod of 4cm in length and 0.5 cm in diameter is generally used. The end faces of rod are strictly made parallel, grounded and silver polished. The one end face is fully reflecting and other end is partially reflecting. A helical Xenon flash tube is surrounded the ruby rod with high voltage power supply. It provides pumping light to raise Cr3+ ions to upper energy level.
Xenon flash tube operates for few milliseconds and produces blue- green light of wavelength 5500 A0. Only a part of energy is used in pumping while rest heats up the apparatus hence cooling arrangement is used. Working: In normal state, Cr3+ ions are in ground level E1. When ruby crystal is irradiated by Xenon flash light, Chromium atoms are excited and pass to upper energy level E3. Now few excited Chromium atoms return to ground level E1 and other to energy level E2. The transition from E2 to E3 is radiation less and difference of energy is converted into heat. Most of excited atoms in E3 return to ground level E1 spontaneously and remaining atoms go to the metastable state E2. After few milliseconds, E2 level becomes more populated than level E1. Hence population inversion (N2 > N1) is achieved between E1 and E2. Population inversion state is not stable. The spontaneous emission (due to jumping of Chromium atoms from E3 to E1) can cause the stimulated emission and thus knock out another photon i.E. There is no need of external source to trigger the laser action. These two will knock out two more photons and their total number will be four and so on. The photon beam parallel to the ruby rod grows in strength and bursts out through the partially reflecting end, giving a fine and intense laser beam of pink colour and of wavelength 6943 A0.
Q. State the applications of optical fiber?
1. It is used for communication like telephone, teleconferencing, and cable TV 2. It is used to transmitted the digital data generated by computer 3. It is used in security system 4. It is widely used in military for communication, command and controlled link on ship and aircraft 5. It is used in a medical for endoscopy for visualization of internal portion of human body 6. Fiber sensor are used to measure the temp, pressure, rotary and linear position and liquid level
Q. Properties and application of laser
1. Directionality: – Laser is a highly directional. It emits light only in one direction. 2. Monochromaticity: – It produce essentially single wavelength (frequency). It is highly monochromatic than ordinary light. 3. Coherence: – It is highly coherent. It possesses high degree of ordering of light. It has a constant path difference. 4. Brightness: – It is highly intense and brighter. 5. Power density:- Power density is very high (i.E. ≈ 108 to 1012 watt).
Application: 1) Medical Application:- i) The affected part of the body can be burnt out by irradiating with Laser hence it is used in treatment of cancer. Ii) It is useful in many micro surgeries like surgery of eyes, brain surgery, bloodless surgery can be done with use of laser. 2) Military Application:- Laser used in many weapons. Other Application:- 3) It is used in determine the path of mode object and shape of the object. 4) The process like cutting, drilling the process can done by laser 5) Laser can be used to measure the distance between the two objects. 6) It is used for data storage in computer. 7) It is also used in printer. 8) It can used to study of structure of atom and molecules. 9) Because of high energy density in laser beam, information can be sent on a long distance without much loss of energy i.E. It is used for communication.
Q -what is diffraction? Distinguish between Fresnel and Fraunhofer diffraction
Defination -The bending of light around an obstacle placed in its path and spreading of light wave in to the geometrical shadow of an object is called
Fresnel diffraction:
1.Diffraction phenomenon in which either the source of light or screen or both are at finite distance from the obstacle or the aperture is known as Fresnel diffraction 2. No lenses are used to make the rays of parallel or convergent 3. The incident wave front is either spherical or cylindrical
fraunhofer: 1. Diffraction phenomenon in which the source of light and the screen are at effectively infinite distance from the obstacle or the aperture known Fraunhofer diffraction 2. Convex lenses are used 3. The incident wave front is plane in which rays of light are parallel to one another
Q bernoullis equation
When a non-viscous and incompressible liquid flows in streamline the sum of pressure energy, kinetic energy and potential energy per unit mass at any point in streamline remains constant
consider a liquid flowing through a pipe
let A1 and A2 are the cross-sectional area at point A and B respectively
1.P1 and P2 are the pressure of the fluid at point A and b respectively
2.V1 and V2 are the velocity of the fluid at point A and B respectively
3.H1 and h2 are the velocity of the fluid at point A and B respectively
P is density of liquid
this is the required Bernoulli’s equation. It allows to calculate the pressure energy, kinetic energy and potential energy at any point in the flow of the liquid
Q. Difference between streamline and turbulent flow
Streamline:
1. The smooth flow of fluid with velocity smaller than certain critical velocity (limiting value of velocity) is called as streamline flow or laminar flow 2. In a streamline flow the velocity of fluid a given point is always constant 3. Two streamlines can never intersect they are always parallel hence can never form eddires
Turbulent flow
1. The irregular and unsteady flow of a fluid when its velocity increases beyond critical velocity are called turbulent flow 2. in a turbulent flow the velocity of fluid at any point does not remain constant 3. In a turbulent flow at some points the fluid may have a rational motion which gives raise to eddires