BE (1st Semester)
Examination – Nov-Dec-2006
1. (a) Distinguish between the nuclear, fission reactions. Explian the release of energy during fission eind fusion reactions with examples.
(b) Describe construction, principle and working of Bain bridge mass spectrograph using a well labeled diagram.
(c) (i) A city requires 3000 MWh ©f energy per day and a nuclear reactor supplies it at 20% efficiency. if the reacyor used nuclear fuel U-235. Calculate its daily consumption. Energy released per fission of U-235 is 2MeV.
2. (a) What are laser characteristics? Describe principle and working of He-Ne laser. Why a narrow discharge tube is used in He-Ne laser?
(b) Give principle of propagation of light through optical fiber. Derive an expression for acceptance angle.
(c) (i) A laser beam has a power of 50 MW. It has an aperture of 5*io~’ m and it emits light of wave length 7200 A. The beam is focused with a lens of focal length 0.1 m. Calculate the area and the intensity of image.
(ii) An optical power of 1 MW is launched in to an optical fiber of lebgth 100 m. If the power emerging from the othe end is 0.3 MW, calculate the fiber attenuation.
3. (a) Draw energy band diagrams for n-type semiconductor at 0°k and at room temperature. Show that at o°k Fermi leve lies midway between valence band and conduction band.
(b) What do you understand by Miller indices of a crystal plane Show that the spacing between consecutive planes define by Miller indices (h,k,l) is given by:
(c) (i) A substance with face centered cubic lattice has densi 6250 kg/ m3 and molecular weight 60.2. Calculate the lattii constant a . Given Avogadro No.= 6.02 x 1026(kg-moie) ‘. 4
(ii) What fraction of – conductivity of intrinsic silicon at roc ,temperature is due to.(a) electrons and. (b) holes ? Tl electron and hole mobilities are 0.135 m2 vs and 0.048 m2/ ^respectively.
4. (a) What is Hall effect? Derive expressions for Hall volta andHall coefficient. Mention important applications of H effect.
(b) Write short notes in not more than 250 words:
(i) BCS theory of super conductivity.
(ii) Drift and Diffusion current.
(c) (i) The transition temperature for lead is 7.26 K. T maximum criticalfield for the material is 8xio5 A/M. Lead h to be used as a super-conductor subjected to a magnetic fi< of 10*A/M. What prscautions will have to be taken?
(ii) Determine potential barrier for a germanium junction room temperature. When both the an and pregions are dop to the extent of one atom per io6 germanium atoms. Ator carrier density in Ge is 4.4*1028 P/m3
and intrinsic can density is 2.5*1019 P/m3.
5. (a) What do you mean by internal field? Derive Clausius Moss relationship for cubic solods.
(b) What are Ferromagnetic materials? Discuss the importance ol Hystersis curve. How would you use the hystersis curve for selecting the material for the construction of a permane manget?
(c) (i) The polarisability of ammonia molecule is found approximately by the measurement of dielectric constant as 2.42xio”mcm2/n. and1.74X10?”cm2/n.at 309 K and 448 K respectively. Calculate the orientation polarisabilities for each; tempera ture.
(ii) A magnetic material has a magnetization of 3200 A/m and flux density 0.005 Wb/m2. Calculate the magnetizing force ant the relative permeability of the material.