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Physics : Question Paper Jun 2013 - First Year Engineering (Semester 1) | Gujarat Technological University (GTU)

## Physics - Jun 2013

### First Year Engineering (Semester 1)

TOTAL MARKS: 100
TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.
(2) Attempt any four from the remaining questions.
(3) Assume data wherever required.
(4) Figures to the right indicate full marks.

### Answer the following in short. (One mark each)

1(a) Define reverberation time.(1 marks) 1(b) Give four factors which affect acoustics of building(1 marks) 1(c) What is SONAR?(1 marks) 1(d) Give statement of Hall effect(1 marks) 1(e) Define: unit cell(1 marks) 1(f) What is high temperature super conductor?(1 marks) 1(g) Name the most commonly used methods for preparing nanomaterials.(1 marks) 1(h) Mention the names of any four NDT methods(1 marks) 1(i) Define photovoltaic effect.(1 marks) 1(j) Give two conditions for TIR.(1 marks) 1(k) State the main components of the optical fiber(11 marks) 1(l) What is magnetic levitation?(1 marks) 1(m) Give full form of LASER(1 marks) 1(n) Give unit of thermal conductivity(1 marks) 2(a) Explain I-V characteristics of PN junction diode in forward and reverse bias with respective circuits and graphs. (6 marks) 2(b)(i) Solve the following problems:
(i) A silicon plate of thickness 1mm, breadth 10mm and length 10cm is placed in amagnetic field of 0.5 Wb/m 2 acting perpendicular to its thickness. If 10 mA current flows along its length, calculate the Hall voltage developed if the Hall coefficient is 3.66 x 10-4m3/C
(3 marks)
2(b)(ii) Calculate the inter planner spacing for a (3, 1, 1) plane in a simple cubic lattice whose atomic radius is 0.91?(3 marks) 2(b)(iii) The area of interior surface of an auditorium is 3340 m2. Its reverberation time is 1.5 second. If the average absorption coefficient of interior surface is 0.4 sabine, find the volume of an auditorium. (2 marks) 3(a)(i) Explain in detail:
Nd: YAG Laser
(5 marks)
3(a)(ii) Ultrasonic flow detector with its advantages and limitations(4 marks) 3(a)(iii) A liquid column subjected to ultrasonic waves constitutes an acoustical grating.(2 marks) 3(b) An ultrasonic source of 1 MHz sends down a pulse towards the seabed which returns after 0.55 second. The velocity of sound in water is 1800 m/s. Calculate the depth of the sea and wavelength of the ultrasonic sound. (3 marks) 4(a) List and explain the characteristics of musical sound(3 marks) 4(b) Define the terms atomic radius and packing fraction. Calculate the packing fraction for SC, FCC and BCC structures.(5 marks) 4(c) Explain isotopic effect, critical magnetic field and Meissner effect for superconductors.(6 marks) 5(a) scuss properties and applications of metallic glasses.(4 marks) 5(b) Explain X-ray radiography and its advantages and disadvantages for NDT.(5 marks) 5(c) (i) List applications of nanomaterials.
(ii) What are population inversion and optical pumping?
(3 marks)
6(a) Write short notes on (i) Zener diode (ii) Applications of LASER(2 marks) 6(b) Derive the expression for acceptance angle & Numerical aperture of an optical fibre.(6 marks) 6(c) Discuss the important postulates of free electron theory of metals(4 marks) 7(a)(i) Solve the following problems:
(i) An optical fiber core and its cladding have refractive indexes of 1.545 and 1.495respectively. Calculate the critical angle ?c, acceptance angle?in(max) and Numerical aperture.
(4 marks)
7(a)(ii) Calculate the electrical conductivity of copper. Given atomic weight, density and relaxation time as 63.5, 8.9×103Kgm-3 and 2.48×10-14sec respectively.(3 marks) 7(b) List the differences between step index and graded index optical fiber(3 marks) 7(c) Discuss the piezoelectric method of production of ultrasonic waves with necessary circuit diagram.(4 marks)