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Friday, 28 March 2014

Modern physics-Model question paper for Msc


1(a) Explain the terms time dilation and length contraction. (6 Marks)
(b) In the photoelectric effect, how can a photon moving in one direction eject an electron moving in a different direction? What happens to conservation of momentum? (6 Marks)
(c) How does the total intensity of thermal radiation vary when the temperature of an object is doubled? (4 Marks)
(d) In a nuclear reactor, each atom of Uranium releases about 20 MeV when it fissions. What is the change in mass when 1 kg of Uranium is fissioned? (4 Marks)
2(a) What difficulties does the uncertainty principle cause in trying to pick up an electron with a pair of forceps? (4 Marks)
(b) Explain Davisson-Germer experiment. (6 Marks)
(c) Assume that electron beam in a television tube is accelerated through a potential difference of 25 kV and then passes through a deflecting capacitor of interior width 1 cm. Are diffraction effects important in this case? Justify your answer with a calculation. (6 Marks)
(d) The speed of an electron is measured to within an uncertainty of 20000 m/s. What is the size of the smallest region of space in which the electron can be confined? (4 Marks)
3(a) Assuming a pendulum to behave like a quantum oscillator, what are the energy differences between the quantum states of a pendulum of length 1m? Are such differences observable? (6 Marks)
(b) Compare the probabilities for an oscillating particle in its ground state to be found in a small interval at the center of the well and at the classical turning points. (6 Marks)
(c) Does the Thomson model fail at large scattering angles or at small scattering angles? Why? (4 Marks)
(d) The first excited state of sodium decays to the ground state by emitting a photon of wavelength 590 nm. If sodium vapour is used for the Franck-Hertz experiment, at what voltage will the first current drop be recorded? (4 Marks)
4(a) How does a quantized angular momentum vector differ from a classical angular momentum vector? (4 Marks)
(b) The photon has a spin quantum number of 1, but its spin magnetic moment is zero. Explain. (6 Marks)
(c) Explain why the Bohr theory gives a poor accounting of optical transitions but does well in predicting the energies of X-ray transitions. (6 Marks)
(d) A certain excited state of an atom has the configuration 4d15d1. What are the possible L and S values? (4 Marks)
5(a) How do the molecular force constant k compare with those of ordinary springs? What do you conclude from this comparison? (6 Marks)
(b) Explain how equilibrium separation in a molecule can be determined by measuring the absorption or emission lines for rotational states. (6 Marks)
(c) Why does an atom generally absorb radiation only from the ground state, while a molecule can absorb from many excited rotational or vibrational states? (4 Marks)
(d) At what temperature would 25% of a collection of HCl molecules be in the first excited state vibrational state? Ignore the rotational structure. (4 Marks)
6 (a) Would you expect the photoelectric effect to depend on the temperature of the surface of the metal? Explain. (4 Marks)
(b) Explain the salient features of Fermi-Dirac statistics. (8Marks)
(c) Semiconductors are sometimes called 'nonohmic' materials. Why? (4 Marks)
(d) From the Fermi energy for Mg, find the number of free electrons per atom. The molar mas of Mg is 24.3 g and its density 1.74 g/cubic cm. (4 Marks)
7(a) Why is the binding energy per nucleon relatively constant? Why does it deviate from a constant value for low mas numbers? (6 Marks)
(b) Distinguish between a slow neutron and a delayed neutron. (4 Marks)
(c) Explain why a fusion reactor requires a high particle density, a high temperature and a long confinement time. (6 Marks)
(d) A radiation detector is in the form of circular disc of diameter 3 cm. It is held 25 cm from a source of radiation, where it records 1250 counts per second. Assuming that the detector records every radiation incident upon it, determine the activity of the sample in Curies. (4 Marks)
8(a) List some similarities and differences between the properties of photons and neutrinos. (6 Marks)
(b) Why does the radius of a white dwarf or neutron star depend inversely on the number of nucleons? Shouldn't a star with more mater have a larger radius? (6 Marks)
(c) Why is it difficult to obtain precise values for the Hubble parameter and the deceleration parameter? (4 Marks)
(d) A satellite is in a orbit at an altitude of 150 km. We wish to communicate with it using a radio signal of frequency 1000 MHz. What is the gravitational change in frequency between a ground station and the satellite? Assume g does not change appreciably. (4 Marks)

Optics-Model question paper for Msc


1(a) Why light is categorized in the category of electromagnetic waves? (4 Marks)
(b) State and explain Fermat's principle of extremum path and use it to deduce the laws of reflection and refraction of light. (6 Marks)
(c) What do you understand by the power of a lens? Calculate the power of two thin lenses of focal length f1 and f2 separated by a distance d. (6 Marks)
(d) A glass dumbbell of length one meter and refractive index 1.5 has ends of radius of curvature 5 cm. Calculate the position of the image due to reflection at one end only, when the object is at a distance of 40 cm from one end. (4 Marks)
2(a) Define cardinal points of a system of co-axial lenses. Describe how you would determine experimentally the principal planes of a combination of two thin lenses separated by a distance. (6 Marks)
(b) Describe nodal assembly methods to locate cardinal points of a lens system experimentally. Explain its working with particular reference to the characteristics of nodal points. (6 Marks)
(c) What is the advantage of using matrix method in paraxial optics? (4 Marks)
(d) The focal length of each lens of Ramsden's eyepiece is 4 cm by matrix formulation. Find the focal length and determine the positions of the cardinal points. (4 Marks)
3(a) Derive the condition for the combination of two thin prisms to produce mean deviation without net dispersion. Derive an expression for the net mean deviation. (6 Marks)
(b) Enumerate the various defects of image formation by an optical system. Explain the methods of removing them. (4 Marks)
(c) Explain the terms entrance pupil and exit pupil. (6 Marks)
(d) Light travels to a target and back in 0.5 sec in carbon disulphide. Calculate the distance of the target if the refractive index of the carbon disulphide is 1.46. (4 Marks)
4(a) What is the difference between oscilatory motion and wave motion? (4 Marks)
(b) What is normal and anomalous dispersion? Derive Sellmeier's equation for the refractive index of a dielectric medium. (6 Marks)
(c) Prove Snell's law of reflection and refraction taking the oblique incidence of elctromagnetic wave on an interference between two dielectric media. (6 Marks)
(d) Find the velocity of a plane wave in a loss less medium having a relative permittivity of 5 and relative permeability of 1. (4 Marks)
5(a) What are coherent sources? How are they realized in practice? Describe a method for determining the refractive index of a gas using the interference phenomena. (8 Marks)
(b) What are the conditions for sustained interference pattern? (4 Marks)
(c) What will happen if wedge shaped film is placed in white light? (4 Marks)
(d) In a Newton's rings experiment, the diameter of 10th ring changes from 1.4 to 1.27 cm when a drop of liquid is introduced between the lens and the glass plate. Calculate the refractive index of the liquid. (4 Marks)
6 (a) Explain the construction of Fresnel's half period zones. (6 Marks)
(b) Give the theory of diffraction grating. Describe in detail how you would use a transmission grating for measuring the wavelength of light. (6 Marks)
(c) Discus Fraunhofer diffraction pattern of a straight edge. (4 Marks)
(d) An optical filter has a line width of 1.5 nm and mean wavelength 550 nm. With white light incident on the filter, calculate (i) coherent length and (ii) the number of wavelengths in the wave train. (4 Marks)
7 (a) Explain Rayleigh criterion for resolution and discuss it in relation to the resolving power of a microscope. (6 Marks)
(b) What is meant by optical rotation? State any two laws of optical rotation. (6 Marks)
(c) State and explain the law of Malus. (4 Marks)
(d) Calculate the thickness of a double refracting plate capable of producing a path difference of λ/4 between extra ordinary and ordinary waves. Given μo= 1.53 μe = 1.54 and λ = 5890Å. (4 Marks)
8(a) Explain some important properties of hologram. (4 Marks)
(b) Describe various mechanisms of dispersion in optical fibers. Explain the effect of dispersion on the bandwidth of optical communication channel. (6 Marks)
(c)Explain stimulated Raman scattering. How can it be explained using quantum concept? (6 Marks)
(d)At what temperature are the rates of spontaneous and stimulated emission equal? Assume λ = 5000Å. (4 Marks)