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
What do you mean by photo electric effect? Show the laws of photoelectric effect. Illustrate these laws using Einstein's equation of photo electric effect?

Derive a mathematical expression for the force per unit length experienced by each of the two long current carrying conductors placed parallel to each other in air. Hence explain o

Q. Using a figure, show how devaluation affects an economy. Answer: While a currency is devalued from E 0 to E 1  the stability shifts from point 1 to 2. Both money supply and

When two molecules approach each other, the charges in each are disturbed and redistributed in a fashion that the average distance among the unlike charges in the two molecules is

Active network:- It can be described as a network, which contains one or more than single source of e.m.f. in it.

Curie-Weiss law (P. Curie, P.-E. Weiss) A more general shape of Curie's law, that states that the susceptibility, khi, of an paramagnetic substance is associated to its thermo

EXPLANATION: Whenever an interaction occurs among two objects, each object exerts the similar force on the other, but in the opposite direction and for the similar length of ti

Question: What is the colour of the shortest wavelength observable light? Answer: Keeping in mind the actuality that the higher the frequency the shorter the waveleng

Alloying: When an impurity atom of a different size compared to the host atom is placed into the crystal lattice, the impurity atom distorts the resin around it, either by pushing

When a string under tension is set into vibration, transverse harmonic rays propagate along its length. When the size of string is same, reflected rays will also exist. The operati