EX-504-C Electrical and Electronics Materials - May 2024 Question Paper

Under each question, How to answer lists the points an answer should cover, outlined by CampusPrep from the syllabus. Check the details against your textbook.

1. 5 Marks
   aFind the current flowing through copper wire of length $0.2 m$, area of cross section $1 mm^2$ when connected to a battery of $4 V$. Given that electron mobility $4.5 \times 10^{-06} m^2 V^{-1}S^{-1}$ and charge on electron $=1.6 \times 10^{-19} c$. The number density of electron in copper is $8.5 \times 10^{28} m^{-3}$.
   How to answer

   • Drift velocity v_d = mu*E, E = V/L
   • Current density J = n*e*v_d = sigma*E
   • Current I = J*A = n*e*mu*A*V/L
   • Substitute values to get I in ampere
2. 5 Marks
   bIn conductivity materials, prove that $$\frac{1}{\mu_c} = \frac{1}{\mu_I} + \frac{1}{\mu_L}$$ Where $\mu_c =$ Overall drift velocity $\mu_I =$ Ionized impurity scattering limited mobility $\mu_L =$ Lattice vibration scattering limited mobility
   How to answer

   • Define total scattering rate as sum of ionized impurity and lattice scattering rates
   • Relate scattering time tau to mobility mu = e*tau/m
   • Use Matthiessen's rule: 1/tau_c = 1/tau_I + 1/tau_L
   • Obtain 1/mu_c = 1/mu_I + 1/mu_L
3. 4 Marks
   cA dielectric materials contains $2 \times 10^9$ polar molecules/$m^3$ each of dipole moment $1.8 \times 10^{-27} cm$. Assuming that all of the dipoles are aligned in the direction of the electric field $E = 10^5 ax V/m$. Find the polarization the electric susceptibility and the relative permittivity?
   How to answer

   • Polarization P = N*p = N*q*d
   • Electric susceptibility chi_e = P/(epsilon_0*E)
   • Relative permittivity epsilon_r = 1+chi_e
   • Substitute N, dipole moment and E to compute values
4. 7 Marks
   aWhat is meant by polarization? Explain the different types of polarization.
   How to answer

   • Define polarization as dipole moment per unit volume
   • Explain electronic, ionic, orientational polarization
   • Explain interfacial/space charge polarization
   • Give frequency/temperature dependence
5. 7 Marks
   bThe electronic polarizability of Ar atom is $1.7 \times 10^{-40} Fm^2$. What is the static dielectric constant of solid Ar (below $84 k$) if its density is $1.8 gm/cm^3$, Relative atomic mass of Ar $= 39.95 g/mol$.
   How to answer

   • Use Clausius-Mossotti relation for static dielectric constant
   • Compute number density N from density and atomic mass using Avogadro number
   • Substitute electronic polarizability alpha_e
   • Calculate epsilon_r
6. 7 Marks
   aWhat is meant by zone refining and crystal growth? Discuss the Bridgman technique for crystal growth.
   How to answer

   • Define zone refining and crystal growth purpose
   • Principle of segregation and moving molten zone
   • Describe Bridgman technique setup and process
   • Advantages and applications
7. 7 Marks
   bDefine semiconductor laser and its characteristics with their applications.
   How to answer

   • Define semiconductor laser principle of stimulated emission
   • Characteristics: monochromatic, coherent, threshold current, directionality
   • Structure of p-n junction laser diode
   • Applications in communications, storage, medical
8. 7 Marks
   aExplain the electronic properties of Gallium Arsenide and Gallium Phosphide.
   How to answer

   • Crystal structure and direct band gap of GaAs and GaP
   • Electron mobility, band gap energies and optical properties
   • Doping and optoelectronic behaviour
   • Applications in LEDs, lasers, high-frequency devices
9. 7 Marks
   bDifferentiate between the photoconductive and photo voltaic cells.
   How to answer

   • Define photoconductive effect vs photovoltaic effect
   • Compare structure, biasing, working principle
   • Compare characteristics and response
   • Compare applications
10. 7 Marks
    aA Solenoid of $500$ turns per meter is carrying a current of $3 A$. Its core is made of iron, which has a relative permeability of $5000$. Determine the magnitudes of magnetic intensity, magnetizations and magnetic field inside the core.
    How to answer

    • Magnetic intensity H = n*I
    • Magnetic flux density B = mu_0*mu_r*H
    • Magnetization M = B/mu_0 - H approx (mu_r-1)H
    • Substitute n=500/m, I=3A, mu_r=5000
11. 7 Marks
    bCompare the ferromagnetism and antiferromagnetism with the help of suitable diagram.
    How to answer

    • Define ferromagnetism: parallel alignment, spontaneous magnetization
    • Define antiferromagnetism: antiparallel equal moments, zero net moment
    • Compare susceptibility vs temperature, hysteresis
    • Draw M-H / spin alignment diagrams
12. 7 Marks
    aExperiments on a sample show that at $12 K$ a critical field of $15 T$ exist and at $10 K$ the critical field is $18 T$. Calculate the transition temperature and critical field at $0 k$.
    How to answer

    • Use Hc(T)=Hc0[1-(T/Tc)^2] for two temperatures
    • Solve two equations for Tc and Hc0
    • Substitute Hc=15T at 12K and 18T at 10K
    • Calculate transition temperature and 0K critical field
13. 7 Marks
    bWhat is Meissner effect? Describe Type-I and Type-II super conductor and their application.
    How to answer

    • Define Meissner effect: expulsion of magnetic flux
    • Type-I: single critical field, complete Meissner, low Hc
    • Type-II: two critical fields, mixed state, high Hc
    • Applications of each type
14. 7 Marks
    aWhat is super conductivity? Explain the terms critical temperature, critical field and critical current density. Draw necessary diagram.
    How to answer

    • Define superconductivity: zero resistivity below Tc
    • Define critical temperature, critical field, critical current density
    • Explain Silsbee rule and H-T-J critical surface
    • Draw resistance vs temperature and Hc vs T diagrams
15. 7 Marks
    bDefine advantage and application of $SF_6$.
    How to answer

    • Define SF6 gas properties: electronegative, inert
    • Advantages: high dielectric strength, arc quenching, thermal stability
    • Applications in GIS, circuit breakers, insulation
    • Safety and handling notes
16. 14 Marks
    Write a short notes on (any two):

    1. i)Ferrous and Non ferrous alloys.
    2. ii)Conductor for underground cables.
    3. iii)Dielectric strength and dielectric loss.
    4. iv)Specification of $SF_6$ gas for GIS applications
    How to answer

    • Select any two topics from i-iv
    • Give definition, key properties and relevant formulas
    • Mention types, factors and applications
    • Conclude with practical significance