The variation of resistance of a metallic conductor with temperature is shown in figure. (i) Calculate the temperature coefficient of resistance from the graph. (ii) State why the resistance of the conductor increases with the rise in temperature.

Explanation

(i) From graph, corrensponding to point A, let the resistance be `R_(0)` and corresponding to point B, the resistance be R. When temperature changes from 0 to `theta^@C`, the resistance changes from `R_(0)` to R .
Thus change in temperature `= theta - 0 = theta^@C`
Change in resistance `= R - R_(0)`
Temperature coefficient of resistnace,
`alpha= ("change in resistance")/("original resistance" xx "change in temp.")`
`(R - R_(0))/(R_(0) xx theta) = (OC - OA)/(OA xx OE)`
(ii) With the rise of temperature of conductor, the resistance of a conductor increases because the frequency of collision of electrons with ions/atoms of the conductor increases, resulting decreases in relaxtion time `(tau)` of electrons.
As `R prop 1// tau`, so R increases as `tau` decreases.