Factors affecting electrical resistivity, Physics

TEMPERATURE:

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,

                                                        Τ=C/T

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 is atomic holography? Atomic holography: Atomic holography has evolved out of the growth of the fundamental elements of atom optics. Along with the Fresnel diffraction

99 ml of H 2 O is initially at room temperature (20.0 o C). A chilled steel rod at 2.0 o C is placed in the water. If the final temperature of the system is 18.7 o C, what is th

What is physics?

Combination of Resistance: In electric circuits the resistors are interlinked in two ways. Resistance in Series Resistance in Parallel

A 25 N box is pulled vertically upward by means of a cord.Find the acceleration of the box if the tension in the cord is 35 N.

Passing Lane velocity vs time graph Suppose the two cars below. The blue car begins ahead of" the red car. The red car actually begins off the screen.) Because the red car is

what is band gap?

a. Consider an x-ray machine with a step-up transformer consisting of a primary coil of 100 turns and a secondary one with 50000 turns. If the voltage applied across the primary co

Cadmium rods are provided in a nuclear reactor. Why? Cadmium rods are given in nuclear reactors due to when we begin nuclear reactor then more energy is required for start the

Can you please, explain what is ''n'' in this equation: Q=ne?