E45 Electrical Conductivity Lab Report

E45 Electrical Conductivity Lab Report - E45 Lab (April 24,...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon
E45 Lab (April 24, 2008) Norbert Wang Electrical Properties of Materials Abstract This lab experiment’s primary concern is measuring resistivity as a function of temperature and concentration of impurities. Three materials were used, copper as a conductor, germanium as a semi- conductor, and NaCl as an insulator. It was found that the insulator has the highest resistance at a given temperature followed by semi-conductors and conductors. The higher the temperature is raised, the lower the resistance becomes in each material. A higher concentration of impurity in the material generates higher resistance. The main distinction between how conductors, semi-conductors, and insulators conduct electricity is the band gap energy between the conduction and valence bands. Introduction The flow of electrons characterizes electrical current. When a voltage potential creates an electric field across a material, free electrons are accelerated. Materials are made up of an arrangement of atoms with internal energy levels. Electrons from the Fermi level in the atom are allowed to freely move as current. The Pauli Exclusion Principle forbids the acceleration of other electrons locked in their energy states. Levels of electron energy form bands, such as the valence band and conduction band. In insulators and semi-conductors, the valence band is full of electrons and there are extremely few electrons (essentially none for insulators) in the conduction band. The more electrons in the conduction band, the better the material conducts electricity. Theoretically, electrons can freely move inside the material with no resistance but in actuality, dislocations, vacancies, impurities, etc can block electrons from easily passing. This idea is known as
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
residual resistivity. Because it is not very temperature dependent, it cannot define the total resistance of the material. The total resistance is a sum of the residual resistance and a thermal contribution. Conductors Conductors have a very rich conducting band with small band gap energy. Conductors resist current by two factors, residual (ρ r ) and thermal (ρ th ) by the following equation: = + ρ ρth ρr There’s a special temperature in conductors called the Debye temperature. Above it, the thermal resistivity is relatively constant in slope. Resistivity can help engineers measure how pure the conductor is. By calculating the ratio of resistivity at room temperature and at very cold temperature (usually liquid helium 4.2K), one can determine the purity. The reason why an extremely low temperature measurement must be taken is because the thermal resistivity component is essentially zero at that temperature. If the conductor is pure the total resistance is equal to the residual resistance because there are no impurities to get in the way of the flowing electrons. Matthiessen’s rule states that the resistivity at a certain temperature is related to the thermal resistivity at
Background image of page 2
Image of page 3
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 01/21/2010 for the course ENGIN 45 taught by Professor Devine during the Fall '07 term at Berkeley.

Page1 / 13

E45 Electrical Conductivity Lab Report - E45 Lab (April 24,...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online