BE (1st Semester)
Examination, Dec-Jan 2008-09
Note : answer all five questions. Part (a) of each questions is compulsory frompart (b), (c), (d) attempt two parts. Use Ful Physical Constants
Charge of electron ‘e’ = 1.6 x I 0 19C
Mass of electron ‘me’ = 9.0×10-31 kg.
Mass of proton ‘mp’ = 1.6725 x 10′27 kg.
1 a.m.u. = 931 MeV = 6.68 x 10″27 kg.
Boltzmann constant k =1.66×10″27 kg.
Planck constant NA = 1*38 x 10-23 Rk.
Permeability of free space = 6.62 x 10~31 J.sec.
Permittivity of free space ‘ ju c,’ = 8.85 * 10-12 F/m
Q1 (a)What is radioactivity? Explain natural and artificial radioactivity.
(b) Describe the construction of Aston’s mass sepectrograph with necessary theory and show how it can be used in the detection of isotopes.
(c) What do you mean by nuclear reactor? Give the sketch of it. What is the function of control rod? Write two factors which should be considered while selecting the site for nuclear reactor.
(d) Write a short note on the structure of atomic nuclei (any four properties). Assuming that protons and neutrons possess equal masses, calculate how many times nuclear matter is denses than water if nuclear redius is given, by 1.2 x 10~1 A ‘” m where A is the mass number.
Q2 (a)Write one difference between a Hologram and an ordinary photograph.
(b) Explain the terms
(i) stimulated emission (ii) population inversion (iii) metastable state
(c) Give the principle of propagation 6f light through optical fiber. Derive an expression for acceptance angle.
(d) (i) A step index fiber is made with a core of index 1.52, a diameter of 29 k and a fractional index difference of 0.0007. It is operated at a wavelength.’ of 1.3^-m Find V-number.
(ii) An optical filter has a line width of 1.5 nm and a mean wavelength 5501 nm. With white light incident on the filter calculate coherence length and. number of wavelengths in the wave tram.
(a) What are crystalline and amorphous solids?
(b) Define unit cell. Express coordination number and atomic packing densities for Simple Cubic Crystal (SCC), Face Centred Cubic Crystal (FCC) and Body Centred Cubic Crystal (BCC).
(c) Define energy levels and energy bands. Explian with proper diagram, how on the basis of band theory, solids are classified as conductors, insulators and semiconductors?
(b)(i) Find the mobility of electrons in copper assuming that each atoln -on-tributes one free electron for conductor. Resistivity of Cu= 1.7×1 O^ohm-cm, atomic wt. = 63.54, density = 8.96 gm/cc.
(ii) Lead is a face centred cubic with an atomic radius 1.746 A. Find the spacing for 220 planes.
.Q4 (a) Define Hall effect.
(b)Draw a neat and labelled energy diagram of P-N junction at equilibrium. Derive the built in potential barrier
V0 =V1In –n12Nd
(c) What is superconductivity? Explain Meissner effect.Derive Type I and Type II superconductors.
(d) (i) Calculate the value of Hall angle ‘0’for a semiconductor on the basis of the following data
Rh = 3.66x 10-4 m3/C (Hall coefficient)
p = 83 3x 10-3a -m, Bz = 0.5 wb/m2
(ii)In a transistor of common base connection current amplification faptor is 0.9. If the
emitter current is 1 mA, determine the value of base current.
5.(a) Write one difference between polar and non-polar Dielectrics.
(b) What do you understand by dielectric constant? Define dielectric susceptibility. Derive a relation between dielectric constants & dielectric susceptibility.
(c) What are hard and soft magnatic materials? Indicate the properties sought in each case. Give their applications.
(d) There are 1027 HCI molecule per cubic meter in a vapour. Determine the orientation polarization at room temperature i.e. 27° C. If vapour is subjected to an electric field of 106 V/m. The permanent dipole moment of HCI molecule being 1.04 bebye unit show that at this temperature and for such a high field the value
of alpha=mue E / KBT is very much less than unity 1 debye unit = 3.33 x 10″
30 coulomb meter