Why electrical conductivity of metal decreases with increase in temperature?
Answers
We know that resistivity = m / (nte^2)
and e are properties of electrons and remain constant.
METALS
In metals, n i.e., the number of electrons in unit volume of the conductor is almost independent of temperature. However, t i.e., the relaxation time does vary with temperature. When temperature increases, the thermal speed of the electrons increases as well as, the amplitude of vibration of the positive ions inside the metal conductor also increase, about their mean positions. Thus, the collisions between the electrons and the positive metal ions become more frequent and this decreases the relaxation time, t, leading to an increase in the resistivity of the conductor.
Also, the temperature coefficient of metals is positive.
SEMI-CONDUCTORS
The number of free electrons in a unit volume of the semiconductor increases exponentially with an increase in the temperature. This more than compensates the small decrease in, the relaxation time. Also, the temperature coefficient is negative. Thus the resistivity decreases with a temperature increase in semiconductors.
ELECTROLYTES
As temperature increases, the inter-ionic bonds weaken a well as the viscous decrease. Thus the ions can move more freely. Thus the resistivity decreases with an increase in temperature in electrolytes. The temperature coefficient is negative here.
ALLOYS
For alloys, resistivity is very high. The resistivity of nichrome has a very low-temperature dependence. The resistivity of manganin is almost independent of temperature. At 0 K temperature, while metals have almost null resistivity, alloys still, have some residual resistivity.
Answer:on increasing temperature for conductors the elections move more efficiently therefore they collide with each other in less time hence decreasing average relaxation time as we know
Rho = m/ne2t ....where t is avg. Relaxation time
Rho increases
Conductivity =1/rho
Conductivity decreases
Explanation: