THEORY EXAMINATION (SEM–VIII) 2016-17 ELECTRICAL AND ELECTRONICS ENGG. MATERIALS

SECTION – A

Attempt all parts (Short Answer Type)

Fatigue in materials refers to the weakening or failure of a material due to repeated cyclic loading over time, even when the applied stress is below the material’s strength limit.

A unit cell is the smallest repeating structure of a crystal lattice that represents the overall arrangement of atoms in a material.

Polymorphism refers to the ability of a material to exist in more than one crystal structure, while allotropy specifically applies to elements that exist in multiple forms.

Solid materials can be classified based on conductivity into conductors, semiconductors, and insulators.

Fermi energy is the highest energy level occupied by electrons at absolute zero temperature.

Doping is the process of adding impurities to a semiconductor to change its electrical conductivity.

Superconductivity has applications in MRI machines, magnetic levitation trains, and lossless power transmission.

An ionic bond is formed when one atom transfers electrons to another, creating positive and negative ions that attract each other, such as in sodium chloride.

Magnetic induction or flux density is the amount of magnetic flux passing through a unit area perpendicular to the direction of the magnetic field.

Intrinsic semiconductors are pure semiconductors, while extrinsic semiconductors are doped with impurities to increase conductivity.

Questions (Section A)

What is fatigue in materials?

Define unit cell.

What is Fermi energy?

What is doping?

Define intrinsic semiconductor.

SECTION – B

Attempt any five (Long Answer Type)

Superconductivity is a phenomenon where materials exhibit zero electrical resistance and expel magnetic fields below a critical temperature.

X-ray diffraction is a technique used to determine crystal structure by observing how X-rays scatter when passing through a crystal lattice.

Piezoelectricity is the property of certain materials to generate electrical voltage when mechanical stress is applied.

Transistors are semiconductor devices used for amplification and switching, operating based on charge carrier movement.

Polarization in materials occurs when electric dipoles align under an external electric field.

The Hall Effect occurs when a magnetic field is applied perpendicular to current flow in a conductor, producing a voltage difference.

Atomic packing fraction measures how efficiently atoms are packed in a crystal structure.

Stress and strain describe how materials deform under applied forces.

Questions (Section B)

Explain superconductivity.

What is X-ray diffraction?

Define piezoelectricity.

What is Hall Effect?

Explain stress and strain.

SECTION – C

Attempt any two (Detailed Explanation)

Crystal defects are irregularities in crystal structures that affect material properties. These include point defects, line defects, and surface defects.

Seven crystal systems include cubic, tetragonal, orthorhombic, monoclinic, triclinic, hexagonal, and rhombohedral, each with specific lattice parameters.

Magnetic materials are classified into diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic, and ferrimagnetic based on magnetic properties.

Questions (Section C)

What are crystal defects?

Explain seven crystal systems.

Classify magnetic materials.