1. an energy gap of a semiconductor has its fermi level just above valence band of 0.2ev and the energy gap is 1.5ev
a) deduce the type of majority carriers
b) calculate the probability of a hole occupying a state at the top of valence band.

2. effective number of states per unit volume in valence and conduction bands is
n=2(2πm*kbt/h^2)^2/3
where m*=effective mass
m*e=0.02me, m*h=0.05me
i) calculate density of state in valence at room temperature
ii) deduce the concentration of holes in valence at room temperature
note* b and e are subscripts

Space-time metric ds2= -dt2+at2dx2+bt2dy2+ct2dz2 (a)how does the area of a rectangle with vertices at ( x=0, y=0, z=0 ), (1,0,0 ), ( 0,1,0 ) and (1,1,0 ) changes with time? (b) if a photon moving in the x direction starts from the origin at t=1, when does it reach x=l? (ds=0 for the trajectory of a photon.) (c) the proper time for a particle is defined by cd=ds. what is the proper time for a particle to move along the trajectory ( x(t)=t, y(t)=0, z(t)=0 ) from t=0 to 1 ? what is the condition on the parameter a so that the velocity of the particle never exceeds the speed of light ?

What are similarities and differences of reflection, refraction, diffraction and absorption?

Write down two additional questions about earth's magnetic field that will make your presentation more informative.