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Wednesday, 19 February 2014

Astrophysics-Model question paper for MSc/PhD

1(a) Compare the advantages and disadvantages of reflecting and refracting telescopes. (6 Marks)
(b) Why short waves are used for radio transmission at far-off places? (4 Marks)
(c)Using Planck's blackbody radiation law, obtain Wien's law and Rayleigh-Jeans law. (6 Marks)
(d) An object moves towards the observer with a velocity of 1000 km/s. What will be the shift of the H-alpha line in its spectrum. (4 Marks)
2(a) Define luminosity of a star. Derive the relationship between the luminosity and the absolute magnitude of a star. (6 Marks)
(b) Show that the altitude of the pole is equal to the latitude of the place of the observer. (6 Marks)
(c) Define spectroscopic parallax. (4 Marks)
(d) Compute the solar constant if the distance between the sun and earth is 1.6 AU. (4 Marks)
3(a)Explain the concept of grey atmosphere. (4 Marks)
(b) Explain blanketing effect in stars. (4 Marks)
(c)Define equivalent width and total half-width of a spectral line. (6 Marks)
(d) Calculate the bound free absorption coefficients per atom of the neutral hydrogen at n =1 and n=2 levels. Calculate the corresponding absorption coefficients for a singly ionised helium atom. (6 Marks)
4(a)An RR Lyrae  star is observed to have an apparent magnitude +20 in a globular cluster. Calculate the distance of the cluster. (4 Marks)
(b) Discuss some important astrophysical information that were obtained by the event of 1987A supernova. (6 Marks)
(c) What observational features of T Tauri stars lead us to believe that they still are contracting towards the main sequence. (6 Marks)
(d) A star has a luminosity equal to that of the sun. Its surface temperature is 2500 K. Compute the radius of the star in terms of the radius of the sun. (4 Marks)
5(a)Explain how the colour-magnitude diagrams are used to calibrate the galactic distance scale. (6 Marks)
(b) On what evidences can we conclude that stellar associations are extremely young objects? (4 Marks)
(c) Define dilution factor. What is its value in an average emission nebula. (4 Marks)
(d) Describe a method by which the temperature of the central star of a planetary is determined. What kind of temperatures are obtained for these stars? (6 Marks)
6(a) Discuss the present understanding of the velocity distribution of the interstellar clouds. Give the various distribution laws and comment on their merits and demerits. (6 Marks)
(b) Discuss Kahn's model of interstellar cloud collisions and calculate the rate of kinetic energy dissipated by the process. (6 Marks)
(c) List the different nuclear reactions which may be present in the sun. Discuss the solar neutrino puzzle. (4 Marks)
(d) Assuming that 20% of the mass of the sun undergoes transmutation from H to He during its lifetime, calculate how long the sun will shine maintaining its present luminosity. (4 Marks)
7(a) Discuss the general nature of the primary and secondary pulses of a pulsar. (4 Marks)
(b) What do you know about the Galactic distribution of pulsars? Are all the observed pulsars Galactic? Give reasons to support your views. (6 Marks)
(c) Draw a diagram of the rotation curve of the Galaxy and obtain a polynomial in the radial distance r that fits the rotation curve fairly well. (6 Marks)
(d) Write a note on cosmic rays. (4 Marks)
8 (a) Explain the terms density wave, dispersion ring, dispersion orbit and Lindblad resonance. (4 Marks)
(b) Explain how we can compute the masses of elliptical galaxies? What simplifying assumptions are made for such computations? What are the sources of uncertainty? (6 Marks)
(c) Distinguish between strong and weak radio galaxies. (4 Marks)
(d) Using Newtonian mechanics, show that the deceleration parameter q is related to the total energy E of the universe and that the universe is flat when E=0. What is then the density in the universe? (6 Marks)

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