2016-2017 December

What are crystal imperfections Mention any two significance of it .

Concept: Introduction to Crystallography

Write schrodinger’s time dependentand time independent wave equations of matter waves in one dimensional and state physical significance of these Equations.

Concept: Schrodingerâ€™S Time Dependent Wave Equation

Draw the I-V characteristics of a photo -diode. What is meant by dark current?

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

Define super conductivity and critical temperature. Plot the variation of resistance versus temperature in case of superconducting state of the material.

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

What is reverberation time? Discuss sabine formula.

Concept: Reflection of Sound(Reverberation and Echo)

State ‘magnetostriction effect’. Mention any two application of ultrasonic waves

Concept: Magnetostriction Oscillator

Calculate conductivity of a germanium sample if a donar impurity atoms are added to the extent to one part in 10^{6 } germanium atoms at room temperature.

Assume that only one electron of each atom takes part in conduction process.

Given:- Avogadro’s number = 6.023 × 10^{23 }atom/gm-mol .

Atomic weight of Ge = 72.6

Mobility of electrons = 3800` (cm^2) / ( "volts") `**sec**

Density of Ge = 5.32 gm/ cm^{3}

Concept: Type I superconductors

Describe with the necessary theory the davisson and german establishing wave nature of electrons. Calculate the de-broglie wavelength of an alpha particle accelerating through a potential difference of 200 volts given :- mass of alpha

particle = 6.68×10^{-27}kg.

Concept: De Broglie Wavelength

Define the term drift current and mobility of a charge carriers. Calculate the current product in a germanium sample of area of cross section 1 cm^{2 }and thickness of 0.01 m, when a potential difference of 2V is applied cross it. Given :- the concentration of free electron in germanium is 2×10^{19 }/m^{3 } and mobilities of electrons and holes are 0.36 m^{2 }/volts sec and 0.17 m^{2 }/volts sec respectively.

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

Draw and explain the unit cell of sodium chloride (NaCl) crystal determine effective number of NaCl molecule per unit cell and co-ordination number.

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

State application of Hall effect. In a Hall effect experiment a potential difference of 4.5 μV is developed across a foil of zinc of thickness 0.02mm when a current of 1.5 A is carrying in a direction perpendicular to applied magnetic field of 2 tesla. Calculate :-

• Hall coefficient for zinc.

• Concentration of electron.

Concept: Hall Effect

Discuss formation of copper pairs and energy gap in superconductor on the basis of BCS theory.

Concept: BCS Theory (concept of Cooper pair)

State any five factors affecting the acoustics of the building and give the remedies for each.

Concept: Reflection of Sound(Reverberation and Echo)

An ultrasonic pulse of 0.09M Hz sends down towards the sea-bed which returns after 0.55 seconds. The velocity of ultrasonic waves in sea water is 1800 m/sec . calculate the depth of sea and wavelength of ultrasonic pulse.

Concept: Ultrasonic Wave Generation

How does the position of fermi energy level changes with increasing doping concentration in p-type semi-conductor ? sketch diagram.

Concept: Fermi Energy Level in Intrinsic Semiconductors

Explain analysis of crystal structure using Bragg’s X ray spectrometer

Concept: X-ray Diffraction

Find the minimum energy of neutron confined to a nucleus of size of the order of 10^{-14}m. Given mass of neutron = 1.675×10^{-27}kg

Concept: Fermi Energy Level in Intrinsic Semiconductors

Calculate the critical radius ratio of an ionic crystal in ligancy-6 . what is the maximum size of cation in ligancy 6 configuration when size of anion is 2.02A°?

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

What do you mean by group and phase velocity? Show that the de-Broglie group velocity associated with the wave packet is equal to the velocity of the particle.

Concept: De Broglie Wavelength

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