BE (1st Semester)
Examination – Nov-Dec-2009
Q.1(a) What is the number of protons and the number of neutrons in 239PU94and 23SU92?
(b) What do you mean by controlled chain reaction ? Hence explain working of Nuclear Reactors.
(c) What is mass spectrograph ? Explain the construction, ‘ principle and working of Bainbridge mass spectrograph. How can We determine the mass of the individual isotopes ?
(d) (i) The half life of a radioactive substance is 1590 years. In how many years will one gram of pure element, (a) lose one centigram & (b) reduce to one centigram.
(ii) An electron of kinetic energy 5 x 103 eV enters a uniform magnetic field of induction 0.32 Wb/m2 perpendiculars’to its direction of motion. Calculate its velocity and radius of the path.
Q.2.(a)The light beam so emitted by Stimulated emission ir> laser, is monochromatic because :
(i) The all emitted photons are having same energy hv.
(ii) There, is no time difference between two “collisions between the photons.
(iii) The photons emitted are highly directional.
(iv) None of these.
(b) What are the essential components of a laser ? Discuss, the working of semiconductor laser. How does it differ from other lasers and what are their specials uses?
(c) Using a ray diagram, show acceptance angle in optical fiber transmission. Obtain the expression for N.A. in terms of acceptance angle and refractive indices of core and cladding of optical fiber.
(d) (i) An optical fiber has core refractive index of 1.5 and the cladding is doped to give a fractional index difference of 0.0005. ‘ Calculate Cladding refractive index, Critical internal reflection angle, tt>e extern*! critical acceptance angfe and the numerical aperture (NA).
(ii) A typical helium-neon laser emits radiation of A = 6328 A”. How many photons per second would be emitted by a one milliwatt He- Ne laser ?
Q.3.(a) What do you mean by Co-ordination Number and Atomic packing fraction ?
(b) What are Miller indices ? How they are determined ? Hence deduce expression for inter-planner distance in terms of Miller indices with proper diagraim.
(c) Give expression for Fermi-Dirac distribution function. Explain extrinsic semiconductor with’ energy level diagram and discuss charge neutrality condition.
(d) (i) Nickel crystallizes in a FCC crystal. The edge of a unit cell is 3.52 A0., The “atomic weight of nickei is 58.710 kg/ k.mol. Determine the density of metal, (ii) A sample of intrinsic germanium at room temperature hasa carrier concentration of 2.4 x 1019 /m3. it is doped with antimony at a rate of one antimony atom per million atoms, of germanium. If the concentration of the germanium atom is 4 x lO^/m3, determine the hole concentration.
Q.4.(a) What is meant by drift and diffusion current ?
(b) Define Hall Effect. Show that the ratio of Hall electric field Eh to 1 the Electric field E which is responsiblejfor the current in an n- type semiconductor wafer kept An a uniform magnetic field B is, given by
EH/E = B/nep.
(c) What is Meissner Offect ? Give an account of the phenomenon of superconductivity using BCS theory. What are its applications ?
(d) (i) What is a transistor ? Draw neat’ and leveled diagram of pnp transistor in common base configuration.
(ii) What happens when a pn junction is forward biased ? Find potential barrier across a silicon junction at room temperature if p-region has 1021 acceptor atoms/m3 and n-region has 1022 atoms/m3.
Q.5.(a) Write expression for the capacitance of a parallel plate capacitor (area of cross section ‘A’ and separated by a distance’d’) completely filled with a dielectric.
(b) What are soft and hard magnetic materials ? Explain , the properties of paramagnetic, diamagnetic and ferromagnetic substance and compare them.
(c) What do you mean by polarization of dielectrics ? ‘Explain the behavior, of dielectrics under static electric field.
Derive a relation between polarization P and the external electric field E.
(d) (i) A capacitor uses aluminum oxide as the dielectric witn relative permittivity = 8. An effective surface area of 360 cm2 gives a capacitance of S//F Calculate the field strength and the total dipole moment induced in the oxide layer if a potential difference of 15 volts exists across the capacitor.
(ii) In a magnetic material the field strength is found to be 105 ampere/ m. If the magnetic susceptibility of the material is 0.5 k 10*5, calculate the intensity of magnetization and flux density in the material.