Physics 2074
Set A
Attempt all questions:
1) Explain equilibrium current across the pn junction? Use Fermi-Dirac statistics and Maxwell Boltzmann distribution to show the flow n to p is equal to the flow from p to n .How electron current from p to n (that is , associated with minority carries) is not affected by the height of the potential energy barrier? Explain (10)
2) Describe moment of inertia and torque for a rotating rigid body. Find the expression for rotational kinetic and discuss the conditions for conservation. (10)
3) Explain the theory of black body radiation .why this theory needs quantum mechanical interpretation? How this interpretation because experimentally successful ?Explain(10)
Set B
Attempt any eight questions:
4) Explain Hall Effect and discuss the impotence’s of hall voltage while manufacturing electronic devices. (5)
5) Discuss effective’s mass of electrons and holes. (5)
6) Describes electrical conductivity of semiconductors. (5)
7) An oscillating block of mass 250 g takes 0.15 sec to move between the endpoints of motion, which are 40cm apart.
a. What is the frequency of the motion?
b. What is the amplitude of the motions?
c. What is the forces constant of the spring? (5)
8) A current of 50A is established in a slab of copper 0.5cm thick and 2 cm wide .The slab is placed in a magnetic field B of 1.5 T. The magnetic field is perpendicular to the plane of the slab and to the current .The free electron concentration in copper is 8.4 × 1028 electrons/m3? . What will be the magnitude of the gall voltage across the width of the slab? (5)
9) The uncertainty in the position of a particle is equal to the de Broglie wavelength of the particle Calculate the uncertainty in the velocity of the particle in term of the velocity of the de Broglie wave associated with the particle. (5)
10) a) How many atoms states are there in hydrogen with n=3?
b) How are they distributed among the subshells? Label each state with the appropriates set of quantum numbers n, 1,m,m
c) Show that the number of states in a shell, that is ,states having the same n. is given by 2n2 . (5)
11) Copper has a face –centered cubic structure with a one –atom basis .The density of copper is 8.96 g/cm2 and its atomic weight is 63.5 g/mole. What is the length of the unit .cube of the structure? (5)