JNTU
JNTU B.Tech IV SEMI CONDUCTORS AND MAGNETIC MATERIALS Previous Question Paper (November/December - 2018 - R15)
Note: This question paper contains two parts A and B. Part A is compulsory which carries 25 marks. Part B consists of 5 Units. Answer any one full question from each unit.
Part A
Answer all questions.
Define wiedemann franz law.
Answer
The Wiedemann-Franz Law states that the ratio of the electronic thermal conductivity (κ) to the electrical conductivity (σ) of a metal is directly proportional to the absolute temperature (T). This relationship is expressed as:
where L is the Lorenz number, a constant approximately equal to 2.44 × 10⁻⁸ WΩ/K² for most metals at moderate temperatures.
Write an equation for heat flux in thermal conductor? State its importance.
Answer
The heat flux in a thermal conductor is described by Fourier's Law of Heat Conduction, which states that the rate of heat transfer per unit area is proportional to the negative gradient of temperature. The equation is:
In this equation, q represents the heat flux (W/m²), k is the thermal conductivity of the material (W/m·K), and dT/dx is the temperature gradient along the direction of heat flow.
The importance of this equation lies in its ability to quantify how effectively a material conducts heat. It is fundamental in designing cooling systems for electronic components, determining the thermal insulation requirements for industrial equipment, and predicting the temperature distribution within semiconductors during operation to prevent thermal damage or performance degradation.
What is the purpose of understanding band theory?
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Explain Hall effect.
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Give few examples for soft magnetic alloys.
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What is domain wall energy?
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Define permeability.
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Explain permeability of ferritic iron.
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What does maximum energy product mean?
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Define retentivity and coercivity in magnetism?
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Part B
Derive an equation for electrical conductance of metal.
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Explain in detail about the different modes of heat conduction in a metal.
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Derive an equation for wiedemann franz law and explain how thermal conductivity and electrical conductivity changes with increase in temperature?
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Define resistivity? Explain the temperature dependence of the resistivity of copper and various copper-nickel alloys with the help of graph?
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How does the band gap indicate whether a substance is an insulator, semiconductor or conductor? Explain.
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Explain in detail how Hall coefficient can be measured in metals.
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What are elemental semiconductors? What are the limitations of Si elemental conductors?
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What are the advantages of super conductors over conventional conductors? Mention a few applications of superconductors?
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What are ferrites? Discuss different types of ferrites.
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What are the differences between ferromagnetism and ferrimagnetism? Explain in detail.
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What is ferromagnetism? Write short note on ferromagnetic domains.
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State the properties and uses of ferrites.
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What are the factors affecting magnetic permeability of metals and alloys?
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Discuss in detail about different methods to prepare amorphous ferromagnetic alloys.
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What are magnetic colloids? Explain in detail about surfacted and ionic magnetic colloids.
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Write a short note on electrical steels.
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Explain why steel is preferred to make permanent magnets while soft iron is preferred for making electro magnets?
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What are advantages of Fe-Cr-Co magnets over AlNiCo magnets? Give the applications of Fe-Cr-Co magnets?
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Explain how magnetic properties changes with temperature in a permanent magnet.
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Explain about the intermetallic compound permanent magnets and give few examples.
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