Homework 5 Solution

# Homework 5 Solution - Homework 5 Solution Question 14.6...

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Homework 5 Solution Question 14.6 Define the following quantities pertaining to the flow of electrons in a metal conductor: (a) drift velocity; (b) relaxation time; (c) electron mobility. Answer 14.6 (a) The drift velocity v d , is the average velocity achieved by an electron in the presence of a uniform electric field, E . An average value is used since the electron’s motion varies periodically, in a sawtooth manner, as the particle accelerates, collides with positive-ion cores, and reaccelerates. (b) The relaxation time τ , is the average time between collisions of a conduction electron with the positive-ion cores of the metal lattice. (c) The electron mobility, μ, is the proportionality constant relating to the drift velocity to the applied electric field as v d = μ* E . The SI units for μ are m 2 /(V*s). Question 14.8 What structural defects contribute to the residual component of the electrical resistivity of a pure metal? Answer 14.8 Dislocations, vacancies, grain boundaries and impurity atoms are common structural defects that contribute to the small residual component of a pure metal’s electrical resistivity. Question 14.13 What explanation is given for the good electrical conductivity of magnesium and aluminum even though these metals have filled outer 3 s energy bands? Answer 14.13 Although the outer 3 s energy bands in magnesium and aluminum are filled, these metals have good electrical conductivity because their 3 s bands overlap their 3 p bands. In the case of magnesium, the empty 3

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Homework 5 Solution - Homework 5 Solution Question 14.6...

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