2017-2018 December

1) Question no **1** is **compulsory**

2) Attempt ant **three** questions from **Q.2 to Q.6** .

‘Crystal acts as three dimensional grating for X-rays’, explain.

Concept: X-ray Diffraction

Calculate the frequency and wavelength of photon whose energy is 75eV.

Concept: De Broglie Wavelength

Draw the energy band diagram of p-n junction diode in forward and reverse bias condition .

Concept: Fermi Level Diagram for P-N Junction

“Superconductor is a perfect diamagnetic”, Explain.

Concept: Meissner Effect

What is reverberation time? How it is important ? write the factors affecting reverberation time.

Concept: Reflection of Sound(Reverberation and Echo)

A quartz crystal of thickness 1.5 mm vibrating with resonance. Calculate it’s fundamental frequency if the Young’s modulus of quartz crystal is 7.9×10^{10}N/m^{2} and density is 2650 kg/m^{3} .

Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

Mobility of electron and hole in a sample of Ge at room temperature are 0.36 m^{2 }/V-sec and 0.17m^{2 }/V-sec respectively. If electron and holes densities are equal and it is 2.5 ×10^{13 }/cm^{3 }, calculate its conductivity.

Concept: Conductivity, mobility, current density (drift & diffusion) in semiconductors(n type and p type)

With Heisenberg’s uncertainty principle prove that electron cannot survive in nucleus. An electron has a speed of 300m/sec. with uncertainty of 0.01% . find the accuracy in its position.

Concept: Heisenberg’S Uncertainty Principle

Show that fermi energy level in intrinsic semiconductor is at the Centre of forbidden energy gap. What is the probability of an electron being thermally excited to the conduction band in Si at 30℃. The band gap energy is 1.12 eV.

Concept: Fermi Energy Level in Intrinsic Semiconductors

With neat diagram of unit cell , explain the structure of HCP crystal and calculate the no. of ions per unit cell, co ordination no., lattice constant and packing factor of the structure.

Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

State the Hall effect. Derive the expression for Hall voltage and Hall coefficient with neat diagram.

Concept: Hall Effect

What is the working principle of maglev? Explain how it can acquire high speed?

Concept: Applications of superconductors- SQUID, MAGLEV

A hall of dimension 25×18×12m^{3 }has an average absorption coefficient 0.2. find the reverberation time. If a curtain cloth of area 150m^{2 }is suspended at the centre of Hall with coefficient of absorption 0.75, What will be the reverberation

time?

Concept: Reflection of Sound(Reverberation and Echo)

State the piezoelectric effect. With neat circuit diagram explain the principle and working of piezoelectric oscillator .

Concept: Piezoelectric Oscillator

With energy band diagram ,explain the variation of fermi energy level with temperature in extrinsic semiconductor .

Concept: Fermi energy level in extrinsic semiconductors

Explain with example how to determine crystal structure by Bragg’s X-ray spectrometer.

Concept: Bragg’S Law

Obtain one dimensional time dependent time independent Schrodinger equation.

Concept: Schrodinger’S Time Dependent Wave Equation

Define ligancy and critical radius ratio. Calculate critical radius radio for ligancy 6.

Concept: Study of characteristics of unit cell of Diamond, ZnS, NaCl and HCP;

What is the significance of wave function ? derive the expression for energy eigen values for the free particle in one dimensional potential well.

Concept: Wave Function

What is photovoltaic effect? Explain the principle and working of solar cell.

Concept: Applications of semiconductors : Rectifier diode, LED, Zener diode, Photo diode, Photovoltaic cell, BJT, FET, SCR., MOSFET

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