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Fluctuations in a conductor Kshatriya, Amarnath R.

Abstract

Applying purely thermodynamic arguments it has been shown that temperature fluctuations in a sample can be represented by introducing appropriate 'series temperature generator’ or 'shunt heat current generator'. The temperature fluctuations lead to resistance fluctuations in the sample. These resistance fluctuations due to temperature fluctuations can be detected as voltage-fluctuations (temperature noise) by using a sensing direct current through the sample. Statistical-mechanical arguments are used to obtain theoretical expressions for spectral density of heat current fluctuations in a metallic conductor in terms of the macroscopic properties of the conductor. Since the electrons are carriers of heat and electric currents in a metal, heat and electric current fluctuations are correlated. Spectral density of cross-correlation between electric and heat current is derived. Statistical considerations are extended to the calculation of the steady state spectral density of heat current fluctuations between two black bodies in radiative contact. Temperature noise in a system in which there is only a partial correlation between temperatures at different points along the length at any time (isothermal System) is compared with a system in which there is a complete correlation between temperatures at all points along the length at any time (Single Temperature System). Experimental results indicate that for the metal filament used Nyquist theorem can be applied at the operating temperature. For frequencies close to the characteristic frequency of the system it is observed that there is an increase in noise temperature of the filament due to temperature noise.

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