JNTU
JNTU B.Tech III ELECTRICAL ENGINEERING MATERIALS Previous Question Paper (October - 2020 - R16)
Answer any five questions. All questions carry equal marks.
Main
What is polarization? Explain about different types of polarization.
Answer
Polarization is the process of displacement of bound charges in a dielectric material under the influence of an external electric field, resulting in the formation of electric dipoles. The total polarization P is defined as the dipole moment per unit volume.
The different types of polarization are:
- Electronic Polarization: Occurs due to the displacement of the electron cloud relative to the nucleus in an atom. It is independent of temperature and occurs at very high frequencies.
- Ionic Polarization: Arises in ionic crystals due to the relative displacement of positive and negative ions under an applied field. It is also independent of temperature.
- Orientational (Dipolar) Polarization: Occurs in molecules that possess a permanent dipole moment. In the absence of a field, these dipoles are randomly oriented; an external field causes them to align, which is highly temperature-dependent.
- Space Charge Polarization: Occurs in materials containing mobile charge carriers that get trapped at interfaces or grain boundaries, creating a macroscopic dipole moment.
Distinguish between pyro-electric and piezo-electric materials, give example of each.
Answer
| Feature | Piezo-electric Materials | Pyro-electric Materials |
|---|---|---|
| Mechanism | Generates electric charge in response to mechanical stress or strain. | Generates electric charge in response to changes in temperature. |
| Dependency | Dependent on mechanical deformation. | Dependent on thermal flux or temperature variation. |
| Symmetry | Requires non-centrosymmetric crystal structures. | Requires a unique polar axis in the crystal structure. |
| Example | Quartz, Barium Titanate. | Lithium Tantalate, Triglycine Sulfate. |
While all pyro-electric materials are inherently piezo-electric due to their polar crystal structure, the reverse is not always true. Piezo-electric materials are widely used in transducers, sensors, and actuators where mechanical energy conversion is required. Pyro-electric materials are primarily utilized in infrared detectors and thermal imaging sensors where detecting heat fluctuations is the objective.
What is dielectric loss? Explain loss tangent and its significance.
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Explain the concept of anti-ferromagnetism and use of such materials.
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Give the classification of magnetic materials in detail with properties and applications of each class.
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List the differences between hard and soft magnetic materials.
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Draw a typical loop for a ferromagnetic materials and explain. Show the residual magnetism and coercive force on a loop and define them.
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Write a short notes on ageing of magnets.
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What is Intrinsic Semiconductor and Extrinsic Semiconductor? What is the effect of temperature on an extrinsic semiconductor material? Explain.
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What is meant by doping and doping agent? Explain.
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Explain different VLSI techniques.
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Explain about the materials used for electric contacts emphasizing on their properties.
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Explain the effect of moisture on insulation in detail.
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Describe the various applications of Radioactive Materials in Electrical Engineering.
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State the properties and applications of mineral oils in electrical engineering.
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