Question Paper: Sem-1 Applied Physics- I May 17

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## Applied Physics - I May 17

### First Year (Semester 1)

TOTAL MARKS: 80

TOTAL TIME: 3 HOURS
(1) Question 1 is compulsory.

(2) Attempt any **three** from the remaining questions.

(3) Draw neat diagrams wherever necessary.

(4) Figures to the right indicate full marks.

**Q1) Attempt any five**
(15 marks)

**1(a)**Justify us of X-rays in the study of crystals.

**1(b)**Draw the following [231],(213),(102).

**1(c)**Derive APF for FCC

**1(d)**Describe Magnetostriction effect.

**1(e)**The resistivity of Cu is $1.72 \times 10 ^ {-28} $ $m^{-3}$. Calculate the mobility of electrons in Cu. Given that number of electrons per unit volume is $10.41 \times 10^{28}$ $m^{-3}$.

**1(f)**What is cavitation?

**2(a)**What is Fermi level? Show that it is locate at the Center of forbidden energy gap. Find the resistivity of Cu assuming that each atom contributes one free electron.Consider density = 8.96 gm/ cubic cm, Atomic weight = 63.5, mobility of electron = 43.3 cm2/ V-sec.

**2(b)**Calculate APF for HCP structure.

**3(a)**Derive Bragg’s law and using it calculate the smallest glancing angle at which X- rays of 1.549 Angstrom will be reflected from a crystal having spacing of 4.255 Angstrom.

**3(b)**A metal ring having cross section 5 cm2 and diameter of 20 cm has a coil of 200 turns wound over it. Determine the current required to produce flux of 4 milli weber. Consider the metal with relative permeability as 380.

**4(a)**Explain with neat diagram different phases of liquid crystal. State any two applications of liquid crystals.

**4(b)**Explain in detail “electronic polarization”

**4(c)**Define the term “mobility” Write any formulas to obtain it. Write its unit.

**5(a)**Explain the principle of solar cell. What are the main features of its construction?

**5(b)**What are the conditions of good acoustics? Give some methods to design a hall with good acoustics.

**5(c)**Derive critical radius ratio for ligancy 6.

**6(a)**Explain how to produce ultrasonic waves with the help of piezoelectric effect.

**6(b)**What is Hall Effect? How to find carrier concentration using it in semiconductors?

**6(c)**Calculate reverberation time for an empty hall of size $21 \times 16 \times 10$ m3 with absorption Coefficient 0.106.