# GTU PHYSICS Exam Paper Dec 2011

GUJARAT TECHNOLOGICAL UNIVERSITY BE SEM- I / II Winter Examination-Dec.-2011

Subject code: 110011 Subject Name: Physics Time: 10.30 am -1.00 pm Total marks: 70

Instructions:

- Attempt any five questions.
- Make suitable assumptions wherever necessary.
- Figures to the right indicate full marks.

Q.1 (a) One mark each.

**(i) **Name characteristics of musical sound.

**(ii) **The frequency of ultrasonic waves is_______ .

**(iii) **Define unit cell.

**(iv) **Give one-one example of pentavalent impurity and trivalent impurity.

**(v) **What is the life time of charge carriers in metastable state?

**(vi) **Total internal reflection occurs when a light ray travels from to .

**(vii) **What is persistent current?

(b)(i) Give brief account of temperature induced transformation.

**(ii) **What is SQUID? Explain with diagram.

**(iii) **Define X-Ray fluoroscopy. Also name its applications.

Q.2 (a) Define and explain thermal conductivity. Also derive the equation for 07 thermal conductivity K. Write its units.

(b)(i) Calculate packing fraction for FCC and BCC. 03

(ii) In a Hall coefficient experiment a current of 0.25A is sent through a 04 metal strip having thickness 0.2mm and width 5mm.The Hall voltage is found to be 0.15mV, When a magnetic field of 0.2T is applied. Find: (1) Carrier concentration and (2) Drift velocity of the carrier.

Q.4 (a)(i) What is an LDR? Explain the working and applications. 05

(ii) What is zener diode? How zener diode does operates in reverse bias

condition. 02

(b)(i) X-rays of unknown wavelength give first order Bragg’s reflection at 04 glancing 20^{0} with (212) planes of copper having FCC structure. Find wavelength of X-Rays ,if the lattice constant for copper is 3.615A^{0}.

A Hall has a volume of 2265m^{3}.Its total absorption is equivalent to (ii) 94.85m^{[1]} of open window. What will be effect on reverberation time 03 if audience fills the hall and there by increases the absorption by another 94.85m^{2} .

Q.5 (a) Discuss magnetic field effect and diamagnetic property of 07 superconductor. Prove that ¥_{m} = -1 for superconductor.

(b) (i) Discuss at least three of the engineering applications of ultrasound. 03 (ii) Draw circuit diagram of magnetostriction oscillator and explain the 04 working.

Q.6 (a)(i) Classify the fibres on the basis of refractive index profile, on the 05 basis of modes of propagation and on the basis of materials.

(ii) What is the numerical aperture of an optical fibre cable with a clad 02 index of 1.378 and a core index of 1.546?

(b)(i) A uniform silver wire has a resistivity of 1.54×10^{-8} ohm.metre at 05 room temperature. For an electric field along the wire of 1volt/cm. Calculate (1)drift velocity ,(2) Mobility, (3)relaxation time of electron assuming that there are 5.8×10^{28} conduction electron per metre3 of the material. Given M_{e} = 9.1×10^{-31}kg and e = 1.6 x 10^{-19} coulomb.

(ii) Mention any four names of NDT methods. 02

Q.7 (a) What are metallic glasses? How to prepare them? Write also the 07 names of other techniques.

(b)(i) State and explain Weber-Fechner law. 03

**(ii) **What are Miller indices? Draw crystal planes having Miller indices 04 (210),(101) and (010) for simple cubic structure