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Question 5


5.1​ The electron and hole mobilities in a Si sample are 0.135 and 0.48m2/V-s respectively. ​Determine the conductivities of intrinsic Si at 300 K if the intrinsic carrier concentration is 1.5 x 106 atom/m3. The sample is then doped with 1023 phosphorus atom/m3. Determine the equilibrium holeconcentration, conductivity, and position of the Fermi level relative to the intrinsic level.​(5)


5.2​ Indicate on an energy level diagram the conduction and valence bands, donor and acceptor states and the position of Fermi level for

(i) an intrinsic semiconductor.

(ii) a n-type semiconductor.

(iii) a p-type semiconductor.​​​​​​​​(5)

Question 3


If the velocity of sound in a solid is of the order 103 m/s, compare the frequency of the sound wave λ = 20 Å for (a) a monoatomic system and (b) acoustic waves and optical waves in a diatomic system containing two identical atoms (M=m) per unit cell of interatomic spacing 2.2 Å.​​​​​​(10) 


Question 4


4.1. ​The conductivity of silver is 6.5 x 107per Ohm per m and number of conduction electrons per m3 is 6 x 1028. Find the mobility of conduction electrons and the drift velocity in an electric field of 1 V/m. Given m = 9.1 x 10–31 kg and e = 1.602 x 10–19 C.​​​​​​​(5)


4.2​ What is Lorentz number? The thermal and electrical conductivities of Cu at 200C are 390 Wm-1K-1 and 5.87 x107W-1m-1 respectively. Calculate Lorentz number.​​       (5)​

Question 1​​​​​​​​​​​​


Compute the net potential energy of a simple Na+Cl- pair. The equilibrium distance between the ions is 0.28nm. The potential energy due to repulsion between electron sis given by Ur = β/r8​​​(10)

Question 2

2.1 α-Co has an hcp structure with lattice spacings of a= 2.51 A0 and c = 4.07 A0, β Co is fcc, with a cubic lattice spacing of 3.55 A0. What is the difference in density between the two forms?​​(5)

2.2 Sodium transform from bcc to hcp at about T = 23K. Assuming that the density remains fixed, and the c/ ratio isideal, calculate the hcp lattice spacing given that the cubiclattice spacing a' = 4.23 A0 in the cubic phase.      ​​​​​​​​(5)

an electric fan is rotating at 3.0 rad/s when at time t=0 it begins to constantly accelerate at 2.00 rad/s^2. The initial linear acceleration of the edge of the spinning part of the fan has a magnitude of 1.30 m/s^2. What is the radius of the spinning part of the fan?

How much work is needed to decrease the distance between a +15 µC charge and a -20 µC charge from 1 m to 0.25 m?

A light metal rod of length 0.8m and radius 2 cm is clamped at one end and loaded at

the free end with 6kg. Calculate the depression at the free end.


There are two trains A and B. Both trains start travelling to each other from stations Pres

reaches station Q in a total of 3 hours, while train Breaches station Pis a total of 3 cuccs 16

train A is 90 km/h Trains A and B rua ca two different railroads paralely in the opposite dosto the

trains C and D. respectively. Train A passed train C, which was in the seed

B passed train D, which was running at the speed of 67 km in 5 seconds. The best d

to train C is 3:1, and that between train B to train D is 5:4 In what time second did spatch

both were running in the same direction?

Obtain the expression for the dc component of the diode current in case of p - n juction
microwave detector. Determine its value if
the diode is exposed to microwave signal of
V= cos wt, Io =10^-6 A and a =40.
draw the {110} family of planes in cubic and tetragonal unit cell?
Copper has a Debye temperature of 340 K and a Fermi temperature of 81000 K. At
what temperature will the contribution of the vibrations of the crystal lattice (within
the Debye theory) and that of the conduction electrons (within the free electron
theory) to the specific heat become equal?
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