InterviewSolution
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InterviewSolution
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Show, on a plot, variation of resistivity of (i) a conductor, and (i) a typical semiconductor as a function of temperature. Using the expression for the resistivity in terms of number density and relaxation time between the collisions, explain how resistivity in thc casce of a conductor increases while it decrcases in a semiconductor, with the rise of temperature. |
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Answer» Solution :Variation of resistivity `rho`T of (i) a conductor, and (II) a typical semiconductor as a function of temperature T has been shown here. The resistivity of a material is given by the relation ` rho = (m)/(n e^(2) tau)` When the temperature rises, the number density of conduction electrons (n) in a conductor does not materially change but amplitude of atomic/molecular vibrations increases and, consequently, frequency of collisions with electrons increases. As a RESULT, relaxation period decreases and consequently resistivity of the conductor increases. The resistivity of a semiconductor decreases on increasing the temperature. In semiconductors, the number density of electrons (n) increases rapidly with rise in temperature due to TRANSFER of electrons from valence level to conduction level on ACCOUNT of high kinetic energy of free electrons. However, the EFFECT of decrease in relaxation period is not of much consequence. Due to increase in value of n, the resistivity decreases. 
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