**BE (2 ^{nd} Semester)**

** Examination-2005 **

** Basic Civil Engineering**

**UNIT- I**

Q. 1 (a) Beta ray emitted by radioactive substance is

(i) A pulse of electromagnetic wave.

(ii) An electron detached from an orbit outside the nucleus.

(iii) An electron, emitted by the nucleus as a result of decay of a neutro inside the nucleus.

(b) Discuss the trajectory of a charged particle Moving with uniform velocity traversing uniform magnetic induction B if

(i) Vo is parallel to B,

(ii) Vo is perpendicular to B, and

(iii) Vo makes an acute angle with B.

(c) What is mass spectrograph? Explain construction and working of Bainbridge mass-sepectrograph. How the relative

proportions of isotopes are determined?

(d) (i) Define nuclear fission. Calculate the power output of a nuclear reactor which consumes 10 kg of U per day. Given that the

average energy released per U^{211} fission is 200 MeV.

(ii) Define thermonuclear reaction.

In a thermonuclear reaction 1.00 X 10^{3} kg hydrogen is converted into 0.993 X ^{10-3} kg helium, calculate the energy released

in joule. If the efficiency of the generator be 5%, calculate the electrical energy in, kilowatt hours.

**Unit- ll**

Q.2 (a) What is fiber optics?

(b) What is the main drawback of ruby laser? Explain the operation.of a gas laser with the essential, components. How stimulated

emission takes place with the exchange-of energy between Helium and Neon atoms.

(c) Describe the structuer of a typical optical fiber used in practice. Depending upon the types of propagation in the light wave

guide describe the step-index and graded index multi-mode optical fibres.

(d) (i) Give two engineering applications of laser. Imagine that we chop a ontinuous laser beam (assumed to be perfectly

monochromatic x,, =623.8 nm) into 0.1 ns pulses using some sort of shutter. Compute the resultant line width, bandwidth

anc coherence lengths.

(ii) Mention any two advantageous features of optical fibers which are not found in conducting wires. A certain optical fibei

has an attenuation of 3.5 dB/km at 850 mm. If 0.5 mW of optica power is initially launched into the fiber, what is the power

leve in* /up* Wafter 4 km.

**Unit-III**

Q.3 (a) Define crystal lattice, basis and crystal structure.

(b) What is co-ordination number? Calculate the co-ordinatior number for simple cubic, bcc and fee lattices. Also show that fo

bcc and fee crystal structures, the, lattice constants are given

*a _{bee}*= 4r where r is atomic radius.

√3

(c) Describe in short the formation of energy band in solids ant hence explain how it helps to classify the materials into conductors,

semiconductors and insulators (with example in each).

(d) (i) Define fermi energy.

The forbidden gap in pure silicon is 1.1, eV. Compare the numbe of conduction electrons at temperatures 37°C and 27°C.

(Given k the -Boltzinan constant = 8.6 X 10-^{5}eV/Kelvin).

(ii) Calculate the current produced in a small germanium plat’ ofarea.lcm^{2} and of thickness 0.3 mm when a potential difference

of 2 V is applied across the faces. Given concentration of free electrons in Ge is 2 X 10^{19}/m3and mobilities of electrons

and hole: are 0.36 m^{2}V-s and 0.17 m^{2}/V-sec. respectively.

**Unit-IV**

Q.4 (a) Conduction electrons have the mobility higher than holejs because they

(i)are lighter

(ii)have negative charge

(iii)need less energy to move them

(iv)experience collision less frequently

(b)Explain Hall effect and its importance. Show that the rat on of Hall voltage .E_{H} to E which is responsible for the current in

a n-type semi conductor wafer kept in an uniform.magnetic field 3 is given by

E_{H}* = B*

E *nep*

(c) Draw a neat energy band diagram for npn transis unbiased and draw circuit diagram when biased in com mode.

Deduce expression for current gain a *dc* Explain why in a transistor emitter is heavily doped, base is thin and lightly doped

and collector area is larger?

(d)Write short notes on any two

(i) BCS theory of superconductivity

(ii) Soler cell

(iii) Photoconductivity

**Unit-V**

Q.5 (a)Define magnatic susceptibility.

(b)Explain the behaviour of dielectrics under static elect ic fields. Derive a relation between polarization P, the external

electric field E and displacement vector D.

(c)Derive Clausius-Mosotti equation for non polar solid 3 having cubic crystal structure.

The atomic weight and density of sulphar are 32 dnd 2.08 gm/cm^{3}respectively. The electronic polarizability of thei atom

is 3.28×10^{-40} F/m. If sulphar solid has Cubical symmetry, /vhat will be its relative dielectric constant.

(Given e=8.854 X 10″^{12} F/m)

(d)Distinguish between paramagnetic, diamagnetic and ferromagnetic substances. Also discuss briefly the terms

antiferromagnetism and ferrimagnetism on the basis of magnetic dipoles of the atoms.