Question 1

Q.1. Define resistivity and factors affecting resistivity.

Accepted Answer

Resistivity (ρ) is the intrinsic resistance of a material per unit dimensions (R = ρL/A, unit Ω·m); it is affected by temperature, impurities/alloying, mechanical strain, and crystal structure defects.

Question 2

Q.2. Define skin effect in conductors.

Accepted Answer

Skin effect is the tendency of alternating current to concentrate near the surface of a conductor, with current density decaying exponentially with depth, effectively reducing the useful conductor cross-section at high frequency.

Question 3

Q.3. Compare the dielectric properties of solids and liquids.

Accepted Answer

Solid dielectrics generally have higher dielectric strength and permittivity, and better mechanical support capability, while liquid dielectrics self-heal after breakdown, fill voids completely, and provide simultaneous cooling, but are prone to contamination.

Question 4

Q.4. Write properties of electrical insulating materials.

Accepted Answer

Good insulating materials require high resistivity and dielectric strength, low dielectric loss, adequate mechanical strength, thermal stability at operating temperature, and resistance to moisture and chemical degradation.

Question 5

Q.5. Explain superconductivity.

Accepted Answer

Superconductivity is the complete disappearance of electrical resistance in certain materials below a critical temperature Tc, accompanied by expulsion of magnetic flux (Meissner effect).

Question 6

Q.6. Define Curie-Weiss law.

Accepted Answer

The Curie-Weiss law states that the magnetic susceptibility of a paramagnetic material above its Curie temperature varies as χ = C/(T - θ), where C is the Curie constant and θ the Curie-Weiss temperature.

Question 7

Q.7. Discuss the effect of temperature on the conductivity of materials.

Accepted Answer

For metals, conductivity decreases with rising temperature (more lattice scattering); for semiconductors and insulators, conductivity increases with temperature as more carriers are thermally excited across the band gap.

Question 8

Q.8. Define relaxation time of electrons in a conductors.

Accepted Answer

Relaxation time (τ) is the average time between successive collisions of a conduction electron with the lattice, during which the electron is accelerated by the applied field; it directly determines mobility and conductivity (σ = ne²τ/m).

Question 9

Q.9. Why silicon (Si) is preferred over Germanium (Ge) for semiconductors mat…

Accepted Answer

Silicon is preferred over germanium because of its larger band gap (1.1 eV vs 0.67 eV) giving lower leakage current and higher operating temperature, its stable native oxide (SiO₂) enabling planar fabrication, and its greater abundance/lower cost.

Question 10

Q.10. The intrinsic semiconductor carrier density is 1.5×10¹⁶ m⁻³. If the mob…

Accepted Answer

Using σ = ni·e·(μe + μh) with ni = 1.5×10¹⁶ m⁻³, μe = 0.13 and μh = 0.05 m²V⁻¹s⁻¹: σ = 1.5×10¹⁶ × 1.6×10⁻¹⁹ × 0.18 = 4.32×10⁻⁴ S/m.

Question 11

Q.1. Explain the concept of defects in crystalline solids. How do defects inf…

Accepted Answer

Crystalline defects — point (vacancies, interstitials, substitutionals), line (dislocations), surface (grain boundaries) and volume defects — disrupt lattice periodicity; they increase electrical resistivity through electron scattering, while strengthening or weakening mechanical properties depending on type and density.

Question 12

Q.2. What is Hall effect? Derive the relation between hall coefficient and ca…

Accepted Answer

The Hall effect is the development of a transverse voltage across a current-carrying conductor placed in a perpendicular magnetic field; balancing the magnetic and electric forces on carriers yields the Hall coefficient RH = 1/(nq), inversely proportional to carrier density.

Question 13

Q.3. Classify the magnetic material with examples. Also distinguish between s…

Accepted Answer

Magnetic materials are classified as diamagnetic (Cu, Bi), paramagnetic (Al, Pt), ferromagnetic (Fe, Ni, Co), antiferromagnetic (MnO) and ferrimagnetic (ferrites); soft magnetic materials have narrow hysteresis loops for cores, hard materials have wide loops for permanent magnets.

Question 14

Q.4. Define the process of electron scattering. What are the different factor…

Accepted Answer

Electron scattering is the deflection of conduction electrons from their field-driven paths by lattice vibrations, impurities, defects and boundaries; it is influenced by temperature, purity, crystal perfection, and specimen dimensions, and directly limits mobility and conductivity.

Question 15

Q.5. Calculate the intrinsic concentration of charge carriers at 300 K given …

Accepted Answer

Using ni = 2(2πkT/h²)^(3/2)(me*mh*)^(3/4)exp(−Eg/2kT) with the given effective masses and Eg = 0.67 eV at 300 K, the intrinsic carrier concentration evaluates to approximately 4.7×10¹⁸ m⁻³.

Question 16

Q.6. Describe the phenomenon of superconductivity, including its origin, zero…

Accepted Answer

Superconductivity arises from Cooper pairing of electrons (BCS theory) below a critical temperature, producing exactly zero DC resistance and the Meissner effect — the active expulsion of magnetic flux that distinguishes a superconductor from a mere perfect conductor.

Question 17

Q.7. Explain the relationship between current, voltage and resistance in meta…

Accepted Answer

Ohm's law states V = IR: current through a metallic conductor at constant temperature is proportional to the applied voltage, with resistance R the proportionality constant; microscopically this follows from the drift of free electrons with a field-proportional drift velocity limited by scattering.

Question 18

Q.1. (a) Why skin effect is absent in DC fields? (b) Derive the relation betw…

Accepted Answer

(a) Skin effect requires a time-varying flux, so it vanishes for DC; (b) solving Maxwell's equations in a good conductor yields exponentially decaying current with skin depth δ = 1/√(πfμσ); (c) for σ=10 S/m at 10 MHz, δ ≈ 5.03 cm.

Question 19

Q.2. (a) Describe the energy band diagram of metal, semiconductor and insulat…

Accepted Answer

(a) Metals have overlapping/partially-filled bands (no gap), semiconductors a small gap (~1 eV) and insulators a large gap (>3 eV) between valence and conduction bands; (b) with the given data σ = e(nμe + pμh) ≈ 0.294 S/cm, giving resistivity ρ ≈ 3.4 Ω·cm.

Question 20

Q.3. Explain polarization in dielectric. Discuss electronic, ionic and molecu…

Accepted Answer

Dielectric polarization is the field-induced separation/alignment of bound charges producing a net dipole moment per unit volume; electronic polarization is electron-cloud displacement in all atoms, ionic polarization is relative displacement of oppositely charged ions, and molecular (orientational/dipolar) polarization is field alignment of permanent molecular dipoles.

Question 21

Q.4. (a) Explain the term magnetostriction as applied to ferromagnetic materi…

Accepted Answer

(a) Magnetostriction is the small elastic strain a ferromagnetic material undergoes when magnetized (and the converse stress-induced change of magnetization), responsible for transformer hum and used in transducers; (b) the energy stored per unit volume equals the area ∫H·dB, so the total energy in a permanent magnet is obtained from the relevant area associated with the B-H loop, with the (BH)max product characterizing stored energy in the demagnetization quadrant.

Question 22

Q.5. What is semiconductor? What is the difference between N-type and P-type …

Accepted Answer

A semiconductor has conductivity between conductor and insulator with a small band gap (~1 eV); N-type material is produced by doping with pentavalent donors (P, As) giving electron majority carriers, P-type by doping with trivalent acceptors (B, Ga) giving hole majority carriers.

Electrical Materials