Question 1

Q.1. Write the unit of electrical and thermal conductivity.

Accepted Answer

Electrical conductivity is measured in siemens per meter (S/m, or mho/m); thermal conductivity is measured in watts per meter-kelvin (W/m·K).

Question 2

Q.2. Write the name of all possible polarization in water molecules (H₂O).

Accepted Answer

Water molecules exhibit electronic polarization, ionic (atomic/vibrational) polarization, and — because H₂O has a permanent dipole moment — orientational (dipolar) polarization.

Question 3

Q.3. Show the total stored magnetic energy in a permanent magnet on its B-H l…

Accepted Answer

The stored energy of a permanent magnet appears in the second (demagnetization) quadrant of its B-H loop; at any operating point the stored/available energy density corresponds to the B×H rectangle area, maximized at the (BH)max point.

Question 4

Q.4. Define relaxation time of electrons in a conductor.

Accepted Answer

Relaxation time (τ) is the mean time between successive scattering collisions of a conduction electron, determining mobility (μ = eτ/m) and conductivity (σ = ne²τ/m).

Question 5

Q.5. A P-type material having majority carrier density 10¹⁶/cm³ is further do…

Accepted Answer

Adding 10¹⁴/cm³ boron (an acceptor) to P-type material with 10¹⁶/cm³ majority holes gives p ≈ 1.01×10¹⁶/cm³; by mass action, n = ni²/p = (10¹⁰)²/1.01×10¹⁶ ≈ 9.9×10³/cm³.

Question 6

Q.1. What is the crystalline defects? Define: (a) Point defects and (b) Volum…

Accepted Answer

Crystalline defects are departures from perfect lattice periodicity; point defects (vacancies, interstitials, substitutional impurities) are atomic-scale, volume defects (voids, cracks, inclusions, precipitates) are three-dimensional; point-defect concentrations grow exponentially with temperature, while volume defects coarsen or anneal out with thermal history.

Question 7

Q.2. Write the name of two piezoelectric materials. Also define any two param…

Accepted Answer

Common piezoelectric materials include quartz and lead zirconate titanate (PZT), as well as barium titanate and Rochelle salt; key performance parameters include the piezoelectric charge coefficient (d), electromechanical coupling factor (k), voltage coefficient (g) and mechanical quality factor (Qm).

Question 8

Q.3. Why dielectric constant is complex when a time varying electric field in…

Accepted Answer

Under a time-varying field the polarization lags the field, so permittivity becomes complex (ε = ε′ − jε″), the imaginary part representing dielectric loss; a material with ε = 0.9 + j0.8 is extremely lossy (loss comparable to storage — suited to absorbing/heating applications), while 10.5 + j0.2 is a good low-loss dielectric suited to capacitors and insulation.

Question 9

Q.4. State Curie and Curie-Weiss law. Also write the name of two material whe…

Accepted Answer

The Curie law (χ = C/T) describes ideal paramagnets like oxygen and rare-earth salts; the Curie-Weiss law (χ = C/(T−θ)) describes materials with internal moment interactions, applying to ferromagnets above their Curie point, such as iron and nickel.

Question 10

Q.5. How magnetic materials are classified? Also define following terminology…

Accepted Answer

Magnetic materials are classified as diamagnetic, paramagnetic, ferromagnetic, antiferromagnetic and ferrimagnetic; a magnetic domain is a region of uniform spontaneous magnetization, retentivity is the flux density remaining after the magnetizing field is removed, and spin orientation is the relative alignment of electron spin moments that determines the magnetic order.

Question 11

Q.6. Calculate the conductivity of a semi-conductor material which has:

Accepted Answer

With n = 10¹⁵/cm³ (μe = 1300 cm²/V·s) and p = 10¹³/cm³ (μh = 600 cm²/V·s): σ = e(nμe + pμh) = 1.6×10⁻¹⁹(1.3×10¹⁸ + 6×10¹⁵) ≈ 0.209 S/cm.

Question 12

Q.1. What is skin effect? Why this effect absent at DC fields? Find the skin …

Accepted Answer

Skin effect is the crowding of AC current toward a conductor's surface, absent at DC because no changing flux exists to induce internal opposing EMFs; using δ = 1/√(πfμσ) with σ = 10⁶ S/m, the skin depth is ≈11.25 mm at 2 kHz and ≈3.56 mm at 20 kHz.

Question 13

Q.2. (a) If the conductivity of a semiconductor sample changes with temperatu…

Accepted Answer

(a) With σ(t) = 10⁵ − 10³e^(−0.05t) and R ∝ 1/σ: σ(0) = 99,000, σ(500) ≈ 100,000, giving R(500) = 1000 × 99000/100000 = 990 Ω; (b) metallic resistance rises with temperature because intensified lattice vibrations scatter electrons more frequently, giving near-linear ρ(T) curves whose slopes differ between metals.

Question 14

Q.3. (a) Define following terms of superconducting material: (i) Critical cur…

Accepted Answer

(a) Critical current density Jc is the maximum current density a superconductor can carry while remaining superconducting; the Meissner effect is the active expulsion of magnetic flux (B = 0 inside) on cooling through Tc, distinguishing a superconductor from a perfect conductor. (b) Metals have overlapping/partially filled bands, semiconductors a small gap (~1 eV), insulators a large gap (>3 eV).

Electrical Materials