# CSVTU Exam Papers – BE I Year – Applied physics-II– April-May-2009

BE (1st Year)

Examination, April-May   2009

Applied Physics -II

Useful physical constants

(i) Charge of electron e’= 1.6x 10′9C

(ii)Mass of electron Mi, = 9.0X1CT3 ‘kg

(iii) Speed of light c” = 3. Ox 1(fm/s

(iv) Planck’s constant 77’= 6.62 x 10r14j_ S

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

=8.-6xW-5e(‘/K

(vi)      Mass of proton ‘mp=1.6725x1O’^kg

(vii)     Massof Alpha particle 6.68x10T2‘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 Mg24and Mg25nd the ions are singly charged. Find the distan between the line formed by isotope0 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‘”h2 + k2+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

Dn =  M„KBT

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 1Q26 / 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.105 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 = Mo(H + M)

(d)  (i) The atomic weight and density of sulphur are 32 and .205* gm/ CIT15‘respecticely. The electronic polarizability of atom is’3.28 x 10 40F— 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.