Unformatted text preview: a r ≤ < . Problem 3 Electric dipoles occupy the region R r < of the spherical coordinate system such that their polarization vector can be described by z P P o ˆ = r with o P as a constant. Assume free space everywhere, and obtain the value of the closed surface integral ∫ ∂ ⋅ V S d E r r in which E r is the electric field produced by the dipoles, and V is the volume of a hemisphere of radius R 2 whose center is at the origin and whose north pole is on the zaxis. Problem 4 The resistivity of a conductor is defined as σ = ρ / 1 where σ denotes its conductivity. Show that according to Drude’s model, the resistivity of a conductor increases with the square root of the temperature. (Hint: Consider the mean free path of electrons, that is the distance traveled between two successive collisions.) M. Shahabadi...
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 Spring '11
 Dolatabadi
 Electromagnet, Magnetic Field, spherical shell, Electromagnetics School of Electrical and Computer Engineering University of Tehran

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