BE (1st Semester)
Examination – April-May-2010
1(a) Half life of radioactive element depends upon
(i) amount of the element present
(iv) none of the above.
(b) Describe the theory, construction and working of cyclotron. What are the limitations of a cyclotron ?
(c) (i) The radioactive disintegration constant y of radium D is 1.13 x 10~9 sec-1. How much time a given sample would take to reduce 1/10 of its original value ?
(ii) a Bainbridge mass spectrograph,, the electric field used is 8’x 104 V/m. The magnetic field common to both plates is 0.55 Wb/m2. If the ion source consists of singly ionized Nepn isotopes of atomic masses 20 and 22, calculate the linear separation of the lines formed on the photographic plates.
(d) Explain what is meant by nuclear fusion. Give the account of proton-proton chain and carbon-nitrogen cycle in reaction. Is the energy release per nucleon in fusion fission ? Explain.
Q.2(a) What is meant by step-index and graded index fibrt?
(b) What is the main drawback of ruby laser ? Explain the of a gas laser with the essential components. How : emission take place with the exchange of energy betwee Ne atoms ?
(c) Give principle of propagation of light through opt Derive an exprersion for acceptance angle.
(d) (i) Imagine that we chop a continuouslaser beam (assuci be perfectly monochromatic ?y0 = 623.8nm) into 0.1 ns pulses us sort of shutter. Compute the resultant line wid width and coherence lengths.
(ii) Determine the numerical aperature of a step in< when the core refractive index nt =1.5 and the refractive index n2 = 1.48. Find the maximum angle for of light if the fibre is placed in air.
Q.3(a) D6fine crystal lattice, basis and crystal-structure.
(b) Describe in short: the formation of energy band and hence explain how it helps’ to classify the mat’s conductors, semiconductors and insulators.
(c) What do you mean by intrinsic and extrinsic semio ? Define charge neutrality equation with the help of lav action.
(d) (i) Polonium belongs to SC lattice. If the lattice consts A. Calculate its density. (The atomic mass of polonium is ;
(ii) In a solid, consider the energy level lying 0.01 Fermi level. What is the. probability of this level i occupied by an electron ?
Q.4.(a) ln P-N-P transistor, the collector current is
(i) equal to emitter current
(ii) slightly less than emitter current
(iii) greater than emitter current
(iv) none of the above
(b) Define super conductivity: Explain Meissner effect. Type-I and Type-ll super conductors.
(iii) What is a P-N Junction Diode ? Explain the working Junction diode under forward and reverse biasing. Dre voltage characteristics curve for this diode.
i (d) Write short notes on any two
(iii) Solar Cell
Q.5.(a) Define magnetic susceptibility.
(b) Derive Clausius-Mossotti equation for non polar solids having cubic crystal structure.
(c) What are ferromagnetic materials ? Discuss the importance of Hystersis Curve. How would you use the curve for selecting material for construction of permanent magnets.
(d) (i) The susceptibility of paramagnetic FeC13 is 3.7 x 10 3 at 27°C. What will be the value of its relative permeability Mr at 200°K and 500°K ?
(ii) The atomic weight and density of sulphur are 32 and 2.08 gm/cm3 respectively. The electronic polarizability of the atom is 3.28×10-40 F/m2. If sulphur solid has cubical symmetry, what will be its relative dielectric constant ?