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ELECTRICAL AND ELECTRONIC MATERIALS
1.
2.
Write down the expression for Lorentz no.
What is Hall Effect?
3.
Why does conductivity of metals decrease at higher temp?
4.
Find out the temp at which there is 1 % probability that an electron in a solid will have an energy 0.5 eV above the Fermi energy.(|e|
=1.6 x 10-19 C, KB =1.38 X10-23 J/K)
5.
Calculate the wavelength of light if a material has band gap 2.4 eV.
6.
Differentiate between intrinsic and extrinsic semiconductor.
7.
Why is the slope for intrinsic semiconductor steeper than for n-type extrinsic semiconductor in σ Vs 1/ T curve?
8.
9.
Prove that the probability of occupancy of an energy level by the electron below Fermi level at 0 k is 1.
In two materials the energy gap between the conduction band & valence band is≈ 1 eV & ≈5 eV. Classify the materials electrically.
10. Is Hall Effect affected by sign of the charge carrier? Justify your answer.
11. A current of 200 ampere is established in a rectangular slab of copper of width 2 cm & 1 mm thickness’ magnetic field of induction 1.5
Tesla is applied perpendicular to both current & the plane of the slab. The concentration of free electrons in copper is 8.4 x 10 28 m-3.
Calculate the hall voltage across the slab.
12. Calculate the Fermi energy in Zinc at 0k.The density and atomic mass of Zinc is 7.14 g/cm3 and 65.38amu.
13. Mention one similarity & one dissimilarity between energy level band diagram of silicon & diamond?
14. The concentration of free electrons in copper is 8.4x1028m-3..Calculate the Hall co-efficient
15. According to Drude-Lorentz theory of metals , write down mathematical expression for Wiedmann-Franz law.
16. Mention four electrical properties of materials.
17. In a certain intrinsic semiconductor the mobility of electrons is 0.3xmet 2v-1s-1 ,the mobility of holes is 0.2xmet2v-1s-1 and forbidden
energy gap/band is 0.7ev.Calculate the intrinsic carrier concentration in semiconductor if effective mass of
electrons
and
holes are respectively 0.55 and 0.37 times the rest mass of an electron.
18. Show graphically the variation of resistivity of a pure metal with temperature according to classical free electron theory of
metals.
19. Give the band diagram of insulator, conductor & semi conductor.
20. Show that all the energy levels of a material below the fermi level at 0k are filled up by electrons.
21. What type of semiconducting material is produced when an alloy of aluminium & germanium in the ratio 1: 10 6 is prepared?
22. Draw an expression for the average energy of an electron in metal at 0k in terms of Fermi energy of an electron at 0k.
23. A metallic wire of length 0.6m & diameter 0.4 mm has a resistance 0.10Ω at 300k. Using the above data calculate the Lorentz number
according to classical free electron theory of metals if the thermal conductivity of the metal at 300k is 380 w/mk.
24.
SUPERCONDUCTOR MATERIALS
1. What is Joseph son effect?
2. Show that electric field inside a superconductor is zero.
3. Distinguish between type-1 & type-2 superconductors.
4. What are cooper pairs?
5. What type of magnetism is developed in a superconductor when its temp is lowered below its critical temp?
6. Show the variation of resistance versus the temperature of a superconductor & normal conductor.
7. Distinguish between soft & hard superconductor
8. It is found experimentally that superconducting critical temp of certain material is 8.93 k & critical magnetic induction at 0k is 80.3 x 10 -3
Tesla. What will be the critical current density?
9. .What type of magnetism is developed in a superconducting material below its critical temperature ?
10.
It is found experimentally that superconducting critical temp of indium is 3.4k & critical magnetic induction at 0k is 29.3 x 10 -3
Tesla. What will be the critical current density of indium wire of radius 5 mm at 4k?
11.
Out of MB, FD & BE statistics which type of statistics is applicable to the cooper pairs?
12.
Show that superconducting material exhibits perfect diamagnetism in superconducting state.
13.
Distinguish between superconductor & perfect conductor.
14.
It is found experimentally that the superconducting critical temp of lead is 7.193k & critical magnetic induction at 0k is 80.3 x 10-3
Tesla. What will be the critical current density of lead wire of radius 5 mm at 4 k?
DIELECTRIC MATERIALS
1.
HCL vapor having concentration 1027 molecules /m3 & permanent dipole moment 1.04 Debye , at room temp is subjected to an electric
field of 105 volt/meter. Determine the orientation polarization of HCL from the above data
2.
Given density of iron is 7.85gm/cm 3 and its atomic molar mass is 55.85gm.The dipole moment of iron atom in an iron bar of 5cm long
and1cm2 cross-section area is 1.8x10-23 Amp.m2.. Assume that all the atoms in the bar have their dipole moments aligned. What is the
dipole moment of the bar?
3.
The polarizability of argon is 1.818x10-40 coul2 met/Newton.Calculate the di-electric constant and electric susceptibility
of argon at
NTP
4.
Determine the orientation polarization
of
HCl
6
vapour at room temp (300K) when it is subjected to an electric field of
10 volt/m.Given that concentration of HCl molecule = 10 molecules/m3,permanent dipolemoment of HCl molecule=3.35x10-30coul m
5.
27
What is polarization?
MAGNETIC MATERIALS
1.
What are hard directions?
2.
What is the net spin magnetic moment for Fe +3 ions?
3.
Distinguish between soft & hard magnetic materials
4.
A rare earth metal is ferromagnetic with 7.1 β atom. Calculate its saturation magnetization (at. Wt. =157.26 amu, density=7.8 x 10 3 kg/m3).
5.
Write an expression for the magnetic susceptibility of antiferromaterials at temp more than Neel temp.
6.
What type of magnetism is developed in a superconductor when its temp is lowered below its critical temp?
7.
The radius of an indium wire is 6 mm. The critical temp is 3.4 k & the critical magnetic field is 29.3 x 10 -3 Tesla at 0 k for indium .Calculate
the critical current density in the wire at 2 k.
8.
The magnetic susceptibility of a material at room temp is 0.82 x 10-8. Calculate its magnetization under the action of magnetic induction of
0.25 Tesla.
9.
It is found experimentally that superconducting critical temp of certain material is 8.93 k & critical magnetic induction at 0k is 80.3 x 10 -3
Tesla. What will be the critical current density?
10. Write an expression for the smallest value of the magnetic moment, an electron can posses & calculate its value
11. London’s penetration depth in certain superconducting material is 390 Å at 0k. Calculate the magnitude of magnetic induction at a depth of
400 Å at 0k when a magnetic induction of 0.75T is applied.
12. How can you find out the direction of magnetic moment of a current carrying loop
13.
A paramagnetic material contains 7.8 x 1027 ions /m3 with magnetic moment 0.3μB . Calculate the magnetization under the action of
magnetic induction of 0.75 Tesla at 300 k .Here Bohr magneton= μ B =eħ/(2me)
14. A material attains the magnetization of 3400 A/m. Under the action of magnetic induction 0.006 wb/m 2. Calculate the magnetizing field,
magnetic susceptibility & relative permeability of the material.
OPTICAL MATERIALS
1.
Write down the expression for critical fiber length.
2.
What is optical pumping?
3.
Determine the frequency difference between the cavity modes of a laser which is 1 m long & contain a gas of refractive index of
1.0204.
4.
Light is attenuated by 0.15 b/km. How long can an optical fiber be used so that it can retain 10% of its initial intensity?
5.
In a step index Fiber the refractive indices of Core and cladding are 1.53 and 1.5 respectively. Calculate the numerical aperture
of the fiber.
6.
The refractive index of the material is 1.54 and the transmission of a di –electric material is 15mm thick to normally incident light is
0.80.Calculate the thickness of material that will yield a transmissivity of 0.70. All the reflection losses are to be included.
7.
In a material transition occurs between a meta-stable state & an energy level of 0.25 eV & the wave length of radiation emitted is
1100 nm. Calculate the energy of the meta-stable state.
8.
Show figuratively the nature of light ray propagating in graded index optical fiber.
9.
What do you mean by optical properties of materials?
10. Give statement of the basic principle involved in the functioning of an optical fiber.
11. Draw the cross sectional views of an optical fiber & show the different components of the optical fiber in it.
12. In a material , electron transition occurs between a metastable state & an energy level of 0.35 ev. The wave length of radiation
emitted in the process is 4200Å. Calculate the energy of the meta-stable state.
13. Distinguish between step index multimode fiber & graded index multimode fiber.
14. Why optical fibers are not affected by electromagnetic radiation?