ch. 18 notes

ch. 18 notes - MSE 209 Ch 18 Electrical Properties I...

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MSE 209 Ch. 18 Electrical Properties I. Resistance A. V=IR B. Resistivity p and conductivity o are geometry independent forms of Ohm’ Law dV/L=1/A*p R=pL/A C. Resisitvity is a material property that can be converted to resistance by multiplying it by the length and cross sectional area. The same can be done with conductivity D. Conductivty varies by 23 orders of magnitude between different materials E. The four fundamental types of materials can be sorted by this II. Aspects of electrical properties A. What moves charge when a voltage is applied - Electrons, holes, ions B. How easily does charge move in a material - Charge mobility C. What happens if charge cannot move - Polarization- dielectric behavior D. Basic equation of conductivity - N- number of carriers (#/m^3) - Q= charge on each carrier C - U= mobility- ease with which each carrier moves (m^2/V-s) E. Mobility describes the “friction” charge experiences as it moves through a material F. Mobilities vary widely in materials - Metals have lower mobility but have much higher carrier density so they conduct better G. Mobility is decreased at higher temperature - This is due to increase in thermal vibrations and lattice irregularities H. Mobility is also decreased by impurities in composition III. Electronic structure of solids A. Band diagrams are shorthand for describing electorn structure = i i i q N μ σ
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