LOYOLA COLLEGE (AUTONOMOUS), CHENNAI – 600 034B.Sc. DEGREE EXAMINATION – PHYSICS V SEMESTER – NOVEMBER 2003 PH 5400 / PHY 400 – GEO PHYSICS
07. 11. 03 Max. : 100 Marks 1.00 – 4.00. |
PART–A
Answer All questions (10 x 2 = 20 marks)
- What is a P – wave? What is it’s velocity?
- State the generalised form of Snell’s law, with a ray diagram.
- Distinguish between surface waves and body waves with respect to their intensity variation with distances
- What are the quantities that can be measured using a Seismometer?
- Bring out the difference between focus and epicentre of an earth-
- Write down the Laplace’s and the Poisson’s equation obeyed by the gravitational potential.
- What is the cause of the main (magnetic) field of the earth according to the dynamo theory?
- Explain briefly, the Gauss method of determining the earth’s magnetic field
- Give the decay schemes of the radio nuclide K40.
- List the two possible sources of heat within the Earth.
PART–B
Answer any FOUR questions (4 x 7 ½ = 30 marks)
- Calculate the bulk modulus and the shear modulus of a material having the following properties.
Density = 4000 kg / m3; dilatational velocity (a) = 10 km / s and shear velocity (b) = 6 km / s.
- Outline the principle and the construction of the strain seismograph with a simple
- a) State the relation between the energy released and the magnitude of an earth-quake
- b) Compare the energies released in earth quakes of magnitudes M = 6 and M = 2.
-2-
- Explain the dynamo theory of earth’s magnetism with the help of the Faraday disc generator.
- Obtain an expression for the variation of temperature with depth below the surface of the earth.
PART–C
Answer any FOUR questions (4 x 12 ½ = 50 marks)
- a) Find an expression for the time of travel of a seismic wave due to refraction in the
outer layers of earth (6 ½ mark)
- b) Derive an expression for the gradient of density in terms of velocities of body
waves (6 mark)
- Discuss the theory of a horizontal seismograph with a neat diagram and explain all
possible cases.
- Explain the working of (I) Hammond and Faller method (of measuring gravity) and
- ii) Worden gravimeter, with neat diagrams (6 + 6 ½)
- Explain the theory of (I) Saturation magnetometer and (ii) alkali vapor
magnetometer. (5 + 7 ½)
- Give the theory of radioactive dating of rocks and minerals using (i) the decay
scheme of Rb87 and (ii) the decay scheme of K40 .