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Ece 152: Electrical Engineering Materials Question Paper

Ece 152: Electrical Engineering Materials

Course:Bachelor Of Engineering In Electrical And Electronics Engineering

Institution: Moi University question papers

Exam Year:2008

ECE 152: ELECTRICAL ENGINEERING MATERIALS

1. The alkali metals lithium through cesium all crystallize in the B.C.C structure, with nearest-neighbour spacings of 3.03, 3.71, 4.62, 4.87, and 5.24 A respectively. The radii of the various monovalent positive ions are 0.68, 0.98, 1.33, 1.48 and 1.67 A respectively. Show that the fraction of space in the lattice outside the compe regions decreases smoothly from 94 percent in lithium to 82 percent in cesium. Calculate the number of free electrons per cubic metre and the average electronic charge enoriv in metallic sodium. Show by solving Poisson's equation that the electrostatic potential is raised by about 12 volts at the centre of a spherical region of 10 A radius inside a sodium crystal for which the free electron density is uniformly 15 percent lower than in the crystal as a whole .

2. Show that an electron of radius R is likely to travel a distance (pi*R*R*N)^-1 before the tube it sweeps out intersects one of a set of N poin per unit volume distributed in space, provided that R is small compared with N^(-1/3).

3. A spherical body of mass M and charge Q moves through a viscous medium at a constant speed (AQE) under the influence of an electric field E in the x direction. A magnetic field is now applied in the z direction, of induction B(z). Set up the equations of motion in the xy plane, and solve for the radius of curvature and the trajectory when the magnetic field is small. (Hint: the velocity component in the x-direction is virtually unchanged.)

Ece 152: Electrical Engineering Materials Question Paper

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