Advanced Optical Physics: Question and Answer Key Set

Engineering Physics-(BAS-101) Short type Question - Ans. Define the Poynting Poynting vector and write its unit. The rate - of flow of energy per unit area in plane a electromagnetic wave, can be described by a vector 3. which is called the pounting vector and represented by 3.ve. Poynting SEXH unit w/m² 2 The light rays from two independent bulbs do not Show interference, give the reason. Two indepondent bulbs can not maintain constant Phase relation between them be. can not be coherent therefore could not produce interference pattern. 3 State the Re -Rayleigh criteria of Resolution: According to Rayleigh criteria, two point sources are resolved by an optical instruments (microscope, prism, telescope, grating)etc) when the central maxima in diffration pattern of one fall over the first maxima in the diffration of the other and vice-versa: ④ what is an optical fibre? How does light signal propagates 4 Through it. An optical fibre 16 a waveguide medium ion which waveguide informations trasmitted from one place to an other place in the form of light. light. It works on the principle of total internal Reflection (TIR). 4 Core aris Cone adding stcladding optical sing nals ⑤ Define the concept 5 - of skinbdepth for high and low frequency of wavelength waveforms. The skin depth is define as the depth at which the electric field strength is reduces to (Ve) times of its lontial value. The skin depth στ depth of penetration is deproted by S 18= = attenuation constant 1 unit 4/m (Neper/m) The skin depth depends upon the frequency of Emwave 1-e frequency is high skintdepth will be low and frequency is low skin depth will be high what is the compton effect and compton shift? When a monochromatic beam of high energy photons is by electron at different scattering angles Scallered by the scattered x-rays had wavelength slightly longer than the incident X-rays 7ο The change in wavelagh 107= λ-λο is called compton shift. The phenomenon of scattering with the change in frequency is called compton effect, This is due to Collision between the high energy. photon and free electron why the centre of Newton's rings in reflected system is dark? Path difference = 2ut cos (1+0) ±7/2, in Newton ring's if T=0 cosr=1, 0=0 1-e at the point of contant t=0, the effective path difference = 7/2. This is the condition of minimum intensity. Hence the central spot of the rings system appears dark. ⑧ what do you mean by of optical fibre. angle and acceptance cone by acceptance angle The maximum entrance angle (Oa) substanded by a raya on the fibre axls at the entry point of the core which suffers total intemal reffection -cladding on the core-cladding boundary is called acceptance angle. The light rays substanded a cone having a full 2Da angle which accepted and transmitted is fibre core is know as acceptance cone. Acceptance Cone Difference between spontaneous and stimulated emission. spontaneous emission Stimulated emission The process of stimulated emission can be colt controlled from outside.. The process of spontaneous emission can not controlled from outside ②incoherent radiation 3 Less intense The emission has broad spectrum 2 Coherent radiation ③ High intense the emission has monochromatic radiation 10, what do you mean by by group velocity? The velocity with which the wave packet propagates average velocity in the medium is known as group velocity: .. It is defined as W = Angular velocity K- propagation constant. refractive index μ and glass plate. of Newton's ring if a liquid of inserted between the plano-convex lens The diameter of the ring is inversely proportional to the what happen the diameter. square root of refractive index of the medium between the Planoconvex lens and plane glass plate, as refractive index increases, diameter of rings decreases. 12 what do you you mean b by dispersive power of grating? The dispersive power of grating is defined as the rate of change of the diffraction angle with the change in the wavelength of light. The ratio do is known as dispersive Power of grating 13 Give the few impotant of application of laser. Medical Laser surgery (bloodtess surgery) in holographic imaging. ③ information processing. CDS, DVDS, laser priters, barcode scanner, laser Pointers. (14) What is displacement current a The displacement current is defined in terms of rate of Change of the electric displacement vector B. The displacement current occurs due to changing electric field and originated from the discharge of the capacitor in a given over overgy State: 18 What is difference between electromagnetic wave and matter wave? Electromagnetic wave EM waves are associated with electric and magnetic field ②EM waves can be radiated into space 3 The velocity of Em wave 3 x108 m/sec. is 4EM wavestravel with the Same velocity (5) The wavelength of Em waves are much large and given by Matter waves matter waves may not be associated with electric and magnetic fields. Matter wave are not neither radiated into space mor emitted by particle The velocity of matter waves are generally less than that of velocity of light ④ matter waves travel with different velocity. The matter waves have shorter wavelength given by 2=4/mv (19) why Population inversion is dessa action. nessony necessary for laser For the laser action in atoms, the stimulated emission. must be greater than the spontaneous • mission, therefore for the production of coherent laser beam stimulated emissión must be required and for stimulated emission atoms must be in the state of Population inversion. 20 Explain the necessity of extended sources? To see the interference effect over the entire film a braod source of light is necessary, En extended source, the light reflected by every point of film reaches the eyes. Hence the entire film can be viewed simultaneously