Factors affecting electrical resistivity, Physics


When the conduction electrons are only scattered by thermal vibrations of thermal ions, then τ in the mobility expression refers to the mean time between scattering events by this process. The resulting conductivity and resistivity are denoted by σT and ρt, where the subscript T represents "thermal" vibration scattering". To find the temperature dependence of the mean free time τ, since this determines the drift mobility. An electron moving with a means speed u is the scattered when its path crosses the cross-sectional area S of a scattering centre. The scattering centre may be vibrating atom, impurity, vacancy, or some other crystal defect. Since τ is the mean time taken for one scattering process, the mean free path l of the electron between scattering process is uτ. If Ns is the concentration of scattering centres, then in the volume SI, there is one scattering centre, that is, Ns=1 thus the mean free path is given . The mass speed u of conduction electrons in a metal can be shown to only slightly temperature dependent. Because the atomic vibrations are random the atoms cover a cross-sectional area A= ∏r2 where a is the amplitude of the vibrations. If the electron's path crosses A= ∏r2 it gets scattered. Therefore the mean time between scattering events is inversely proportional to the area that scatters the electron, that is. As the temperature raises, the amplitudes of the atomic vibrations increases thus,


Where C is a temperature independent constant. Substituting the values we obtain

                                    ΡT= AT

Where A is the temperature independent constant. This shows that the resistivity of a pure metal wire increases linearly with the temperature, and that the resistivity is due simply to the scattering of conduction electrons by the thermal vibrations of the atoms. We term this conductivity lattice-scattering-limited conductivity. The change in resistance of a material per ohm per degree change in temperature is called the temperature coefficient of resistance of that material. The resistance of a conductor changes with temperature according to the law:

                                 Rt = R0 (1+αt)

Where Rt, and R0 are respectively the resistance of the conductor at t degrees and zero degree centigrade's and α, the temperature coefficient of resistance. Based on temperature effects, electrical materials can be classified into two groups:

Positive temperature coefficient of materials: It means that the resistance of some of the metals and alloys increases when their temperature is raised.

Negative temperature coefficient of materials: It means that the resistance of some of the materials, carbon and insulators decreases when their temperature is raised.

Posted Date: 7/21/2012 7:40:51 AM | Location : United States

Related Discussions:- Factors affecting electrical resistivity, Assignment Help, Ask Question on Factors affecting electrical resistivity, Get Answer, Expert's Help, Factors affecting electrical resistivity Discussions

Write discussion on Factors affecting electrical resistivity
Your posts are moderated
Related Questions
Suppose you sound a 1056-Hz tuning fork at the same time you strike a note on the piano and hear 2 beats/second.  You tighten the piano string very slightly and now hear  3 beats/s

Urticaria  :  a skin condition characterized by the development of itchy, raised  white lumps surrounded  by  an  area  of  red inflammation. Osmolarity  :   The osmotic  conc

Yes it is possible at the centre of the earth where the radius is zero .

A block of metal which weighs 60 newtons in air and 40 newtons under water has a density, in kilograms per meter cubed, of: a) 1000 b) 3000 c) 5000 d) 7000

In a certain cathode-ray tube, a beam of electrons, moving at a constant velocity, enters a region of constant electric force midway among two parallel plates that are 10.0 cm long

Demonstrating the effects of the angle of the sun's rays on the quantity of heat and light received by the earth Bend a piece of cardboard and make a square tube 4 cm2 in cros

Friction is a microscopic constant and so macroscopic level area does not matter. But area would matter if the object we''re putting under study was microscopic, which isn''t in o

5 example of Classification and 5 types of Vectors and 3 Dimensional Forces

One of the most important theorems in the quantum physics in the Pauli Exclusion Principle, which is based on the experiment observations. The principle explains that “No two elect

Q. According to classical mechanics, what is the concept of time ? As-per to classical mechanics (i) The time interval among two events has the same value for all observers