**BE (1st Year)**

**Examination, April-May 2009 **

**Applied Physics -II**

** **Useful physical constants

*(i)* Charge of electron e’=* 1.6x 10′ ^{9}C *

(ii)Mass of electron* _{Mi},* =

*9.0X1CT*

^{3}‘kg(iii) Speed of light* c”* =* 3. Ox 1(fm/s *

(iv) Planck’s constant 77’=* 6.62 x 10r ^{14}j_* S

(v) Boltzmann constant ‘k,,* ~l.38xfO~”J1 K* or

*=8.-6xW-5e(‘/K*

(vi) Mass of proton ‘m_{p}=1.6725x1O’^kg

(vii) Massof Alpha particle* 6.68x10T ^{2}‘kg*

(viii) 1 amu* 931* Mev =* 1.66 x 10-27kg *Avogadro number at NTP =* 6.023 x 1Q26/kg_M01 *

Q1*(a)* Why we cannot accelerate from the cyclotron ?

(b) (i) What is Radioactive decay ? Describe three types of decay and the law radioactive decay with mathematical expression.

(ii) 5 gm of radium is reduced by 10.5 mg in 5 years. Calculate the half-li of radium.

(c) (i) Describe construction, principle and working of Bainbridge mass spe trograph with suitable diagram.

(ii) The electric field between the plates of velocity selector is 150 V/c and the magnetic field is 0.5 T. if the source contains the two isotopes magnesium Mg^{24}and Mg^{25}nd the ions are singly charged. Find the distan between the line formed by isotope^{0} on the photo-graphic plate.

(d) (i) Describe principle, construction and working of cyclotron. Give its limitations.

(ii) Magnetic flux density of cyclotron is 2 tesla. What should be the frequency in order to accelerate the proton of mass 1.9 x 10~^{21} kg and charge equal to electron.

Q2(a) Which atoms are used as active centre in Ruby laser and give their percentage in active medium.

(b) Explain construction and working of He-Ne laser with neat diagrams. Why is it necessary to use narrow tubes in this laser

(c) (i) What is a Hologram ? How does it differ from an ordinary photo graph/ Describe it.

(ii) In a laser system, the energy difference between two levels is 0.121 eV. Calculate the wavelength of radiation.

(d) (i) What is meant by acceptance angle for an optical fibre ? Show how it is related to numerical aperature.

(ii) An optical signal has lost 75% of its power after traversing 500m of fibre. What is the loss in dB/km of this fibre ?

Q3. (a) Find the interplanar distance between (110) plane in NaC crystal.

(b) (i) What do you understand by Miller indices of a crystal plane show, that the spacing between consequtive planes defined b} Miller indices (h,k,l) is given by :

^{ M}*‘”h ^{2} + k^{2}+l*

(ii) Find the automatic packing fraction (APF) for BCC and FCC structure.

(c) What is Fermi level ? Show that for an intrinsic semiconductor it lies midway between valence band and conduction band

(d) (i) Prove Einstein’s relation for diffusion coefficient on and- mobility , for negative charge carriers as

*D _{n }= M„K_{B}T*

*e*

where the symbols have their usual meanings.

(ii) A substancewith FCC lattice haS density 6250 kg and molecular weight 60.2. Calculate the lattice constant. Avogadro number is

6.02 x 1Q^{26} /* kg* mole.

*Q4(a)* What are SQUIDS ?Give one application of SQUIDS.

(b) What is Hall affact ?

Derive expressions for Hall voltage and Hall coefficient type semiconductor.

(c) (i) Define Superconductivity. Describe BCS theoi superconductivity.

(ii) The current gain of a transistor is 0.98. What will be its current gain in commonamitter mode ? in the CE-mode, calculate the change in collector current and emitter current corresponding to a change in base current by0.2 mA.

(d) (i) Explain the meanings of parameters of a transistor £ id establish the relationships between them.

(ii) The critical field of Niobium is 1 x 10′* A / m* at 8 K ind 2 x.10^{5}* A /* m at OK. Calculate the transition temperature if the element.

Q5. (a) Define Retentivety and Coercivity in B-H curve for magnetic materials.

(b)What are Polar and Non-polar dielectrics ? Derive Glausius- Mosotti equation for a solid dielectric exhibiting electronic polarizability.

(c) What are diamagnetic, paramagnetic and ferromagnetic substances ? Define magnetic permeability and magnetic. susceptibility and establish the relation :

*B* = _{M}*o**(H* +* M)*

(d) (i) The atomic weight and density of sulphur are 32 and .205* gm/ CIT1^{5}‘respecticely. The electronic polarizability of atom is’3.28 x 10 ^{40}F— M ^{2}– If sulphur solid has cubical symmetry, what will be its relative dielectric constant (ii) A magnetic material has a magnetization of 3,000 A/m and flux density of 0.0044 wbW. Calculat the magnetizing force and relative permeability of the meterials.