1.	Mobility  , where  is drift velocity of carrier and E the applied electrical field;     (2marks) Conductivity  , where n is free electron density and e the electronic charge.        (3 marks)
2.	Ef : Energy of highest filled level in electron energy band structure, at 0 K;                        (2marks) , where k is the Boltzmann constant.                                       (3marks)
3.
4.
5.	At normal incidence, and as a good approximation over a wide range of incident angles, the fraction of light reflected off a surface is is the greater for higher n, the refractive index.                                                               (5marks)

Part B
 

6.	(4marks) where Dl/l arises from change in vacancies concentration, nv/nsites . Denoting the latter (temperature dependent) quantity by C(T) , and the volume of a representative cube of this metal by V, we have                        (3marks) The slope of the plot of lnC(T) vs 1/T gives -Ev/k.                           (3marks) C(T)=C0exp(-Ev/kT) C(660)=C(400)exp[-Ev/(673K*k)] exp[+Ev/(933K*k)]» 9*10-4               (3marks) That is, about one in every thousand lattice sites is unoccupied just below melting occurs.    (2marks) And average distance between two vacancies  lattice constants.                   (2marks)
7.	Planar density                           (1x3marks) Linear atomic density                             (1x3marks) Thus {110} have the highest planar density,                    (2marks)  and <111> the highest linear density.                              (2marks)   The slip systems are therefore ;                          (2+2marks) and the Burgers vector in a slip has the magnitude                                    (3marks)
8.	(i) Max stress expressed by landing gear   (2marks) \landing gear will break on first landing! (1mark) (ii)  is in between T.S. and F.S. ,                    (2marks) \Gear will fail due to fatgue after repeated landing;                       (1mark) (iii)                        (2marks) \Gear should never fail.                                 (1mark)
9.	Griffith's crack model is successful in explaining brittle fracture. (1mark) Microscopic flaws are assumed to have formed during routine production and handling. (1mark)For the ideal case of elliptical cracks, the maximum stress at the tip, when a stress s is applied to the ceramic sample, is  where c is the length of the existing crack, and r radius of currature at the tip.    (4marks) Thus, even if the intrinsic strengths under tension and under compression are comparable, failure occurs at a much reduce tensile stress applied externally, because it induces a greatly magnified  microscopic tensile stress at the tip, which opens up the crack, to increase c, resulting in further amplification of sm, and this process cannot stop until the crack reaches the other end of the sample.                                                                                                    (4marks) Unless the propagating fracture hits another ( pre-existing ) microcrack. Then it may because r suddenly becomes much larger, and the factor (c/r )1/2 is reduced.                          (4marks) Take c~0.1m (microscopic cracks), and r ~1nm (atomically sharp). Then 2(c/r )1/2 ~20 » 10, i.e. tensile and compressive strength differ by an order of magnitude.                          (3marks)
10.	(i) Tempering: (ii) Opacity due to second-phase pores Multiple scattering at pore-glass interface means transmitted image becomes diffuse.            (4marks) Viscosity  (2marks) Given that at T=514+273K=787K, and at T=696+273K=969K, and Then  at T=1204K/931? (3marks)
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