0.19 Even semester2014-midsemester examination answers  (Page 18/3)

Even Semester Mid-Semester Test

Electronic&Electrical Materials_EC1419A

Total Marks:30 Duration:2hrs

Question 1 is compulsory and answer any two out of the remaining three.

Question 1.[15 points]

1. I.What are the MKS units of mass, velocity (v), acceleration (a), force, momentum (p), energy ? Answer: Kg, m/s, m/s 2 , Newton, Kg-m-s -1 , Joules.[1/12+1/12+1/12+1/12+1/12+1/12=1/2Point]

1. II.E = E ₀ exp[j(ωt – kz)]_ This is an equation of a forward travelling wave. Define ω, t, k and z. What is the velocity of propagation ? Answer: ω=radians/s, t=second,k=1/m, z = direction of propagation. Velocity of propagation= ω/k (m/s).[1/10+1/10+1/10+1/10+1/10=1/2Point]

1. III.ψ = ψ ₀ exp[j(ωt-kz)]_This is also a travelling wave. What is ψ ₀ and what is │ψ*ψ│? Answer: ψ 0 is Probability Amplitude, │ψ*ψ│is Probability Density.[1/4+1/4=1/2Point]

1. IV. J = Iω = n[h/(2π)]. This is Bohr’s Law of electrons orbiting the nucleus. Define all the terms. Answer:J→angular momentum, I→moment of inertia, ω→orbital angular velocity, n→principal quantum number, h→ Planck’s Constant.[1/10+1/10+1/10+1/10+1/10=1/2Point]

1. V. Define the four Quantum Numbers n , L, m, s ? Answer: n →Principal Quantum Number, L→Azimuthial Quantum Number, m→magnetic Quantum Number, s→Spin Quantum Number.[1/8+1/8+1/8+1/8=1/2Point]

1. VI. What is COORDINATION NUMBER=N. Si, Ge have DIAMOND Crystal Structure and GaAs is ZINC-BLENDE Crystal Structure. In both crystal structures N = 8. Justify this statement ? Answer: N→number of atoms belonging to each Unit Cell of the crystal structure. In Diamond structure there are (8corner atoms)×(1/8)+(6 face centered atoms)×(1/2)+(4 body centered atoms)= 8 atoms per unit cell.[1/8+3/8=1/2Point]

1. VII. Number density = N ^* = 8/a ³ . What is ‘a’ ? Answer : ‘a’ is the Lattice Parameter.[1/2Point]

1. VIII. For Si,Ge and GaAs ‘a’ = 5.43A°, 5.646A° and 5.6533A° respectively. What is A° ? Answer: A° is Angstrom =10 -10 m = 10 -8 cm .[1/2 Point]

1. VIV. Weight of one ------------_= (AW gm/mole)÷ (N _Avo atoms/mole). Fill up the BLANK . Answer: ATOM [1/2 Point]

1. X. Wt of one atom× N ^* = ρ . Define the terms ? Answer: N*→number density, ρ→weight density.[1/4+1/4=1/2Point]

1. XI. In HYDROGEN ATOM, electron occupies discrete energy states given by E= -13.6/n ² . What is the unit of energy and what is ‘n’ ? Answer: Unit of energy is eV and n→Principal Quantum Number.[1/4+1/4=1/2Point]

1. XII. Hydrogen Atoms produce Lyman Series[2→1,3→1,4→1,5→1,6→1], Balmer Series[3→2,4→2,5→2,6→2,7→2]and Paschen Series [4→3,5→3,6→3,7 →3,8 →3] of Spectral lines. What do the square bracket terms mean? Answer : Square Bracket terms imply transition from Excited States to Ground States.[1/2Point]

1. XIII. FCC has 74% parameter and BCC 68% parameter. What is this parameter and what is the full form of FCC and BCC? Answer: FCC is Face-Centered-Cube and its packing density is 74% and BCC is Body-Centered-Cube and its packing density is 68%.[1/6+1/6+1/6=1/2Point]