The resistance and resistivity concept is one of the most fundamental as well as an essential part of the concept of current & electricity. Here, R is the resistance, p is the resistivity, l is the length and A is the area of cross section of the conductor through which current flows. Hence, resistivity is the resistance of a material body of unit volume. For a cylindrical wire, the area is calculated as follows. Therefore, electrical conductivity \sigma = \frac { 1 }{ \rho }. Power full magnets are made with coils of super conducting materials. Hence, the value of temperature coefficient of resistivity, \alpha is positive. If a conductor is taken such that the values of variables are A = 1 \ \& \ l = 1. Resistance and Resistivity are both important concepts for electrical engineering. The resistance of conductors increases with increase in temperature. Figure shows the behavior of mercury at low temperatures. Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube. A measure of the degree to which a conductor impedes the flow of electric current induced by a voltage. Some even become superconductors (zero resistivity) at very low temperatures. Good conductors of electricity have low value of resistivity and good insulators have a high value of resistivity. What is Resistance . Where, E is energy gap between conduction band and valence band, k is boltzmann’s constant and T is the absolute temperature. Super conductors are used in high speed computing machines. Resistivity of a conductor is defined as the electric resistance of a body of unit length and unit cross sectional area. For most of the metals, resistivity has linear relationship with temperature at normal temperature ranges. The variation of resistivity of insulators with temperature is given by the same relation –. At low temperatures, resistivity increases at a higher power of temperature which can be expressed by the relation –, \rho = \rho_0 \left [ 1 + \alpha ( T - T_0 ) \right ]. The reciprocal of electric resistance is called electric conductance. R = p X l/A, Or, Resistance = Resistivity X length/area.

shows the property of super-conductivity at very low temperatures.
Where, \rho_0 is the resistivity at temperature T_0 (say at 0 ºC), \rho is the resistivity at temperature T and \alpha is the temperature coefficient of resistivity.
Temperature coefficient of resistivity \alpha is different for different materials. Electrical resistivity, represented by the Greek letter ρ (rho), is a measure of how strongly a material opposes the flow of electric current. These materials are called super-conductors. (adsbygoogle = window.adsbygoogle || []).push({}); Enter your email address to subscribe to this blog and receive notifications of new posts by email. The variation of resistivity of semiconductors with temperature is given by the relation –. At low temperatures, semiconductors behave as insulators but at room temperature they behave as conductors. Resistance gives the ratio of the potential difference to current across a conductor at a given time, whereas Resistivity is the ratio of electric field to current density for a material at a specific temperature. Thus, if an element has zero resistance, it means no power loss will occur in the element. Their resistivity decreases more rapidly with increase in temperature as shown in figure (B).

Therefore, their resistivity increases with increase in temperature as shown in figure (A). Temperature Variation of Resistance. We know that, resistivity of a conductor is directly proportional to the temperature, i.e., \rho \propto T . Define Resistance and Resistivity. Energy gap E for insulators is much more than that of semiconductors. Resistivity of insulators decreases exponentially with increase in temperature as shown in figure (B). Since area is dependent upon the shape of the conductor, it has to be calculated according to shape. (See Figure 20.12.) The lower the resistivity, the more readily the material permits the flow of electric charge. Therefore, \sigma \propto \frac { 1 }{ T } . Transmission wires made of super conducting materials may be used for long transmission of electricity without power loss. Conversely, the resistivity of conductors increases with increasing temperature. Electrical conductivity is the reciprocal quantity of resistivity. Materials like mercury, lead, alloys and oxides of certain metals etc. The resistivity of all materials depends on temperature. Therefore, temperature coefficient of resistivity is defined as the rate of change in resistivity by change in unit temperature per unit original resistivity. As the temperature of conductor increases, the conductivity decreases exponentially as shown in figure. The value of the resistivity is the resistance of a unit cube of the material measured between opposite faces of the cube.

Where, \rho is a constant of proportionality which depends upon the material of the conductor. For semiconductors, the value of temperature coefficient of resistivity, \alpha is negative. Resistivity varies with temperature. Materials offer low resistance at low temperatures. Resistivity or specific resistance of a material depends upon temperature of the conductor.

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