As described in in the previous articles the resistance of a material or you can assume a simple metallic conductor , the resistance of such conductor is temperature sensitive. i.e with change in surrounding temperature the resistance value also changes . But how this value changes this is completely depends upon the type of material.
EFFECTS OF TEMPERATURE ON RESISTANCE-
POSITIVE TEMPERATURE COEFFICIENT OF RESISTANCE-
➤When temperature of a pure metals increases then resistance of that metal conductor also increases. The increase is large and fairly regular for normal ranges of temperature. The temperature/resistance graph is a straight line (as shown in figure). This type of phenomenon called positive temperature coefficient of resistance.
 |
| POSITIVE TEMP. COEFFICIENT OF RESISTANCE |
➤ The above figure shows that,
R0 = resistance of material at normal temperature
Rt = resistance of temperature at " t " degree celcious
NEGATIVE TEMPERATURE COEFFICIENT OF RESISTANCE-
➤ In case of some semiconductor material,partial conductors such as carbon and insulating material (such as paper, rubber, glass, mica etc.) the increase in temperature results in decrease the resistance. Hence, insulators are said to possess a negative temperature-coefficient of resistance.
In this case the temp. vs resistance curve becomes downward.you can easily draw this by comparing the above figure which is a upward characteristic.
➤ In case of some alloys the increase in temperature results in increase of the resistance of alloys, though in their case, the increase is relatively small and irregular. For some high-resistance alloys like Eureka (60% Cu and 40% Ni) and manganin,the increase in resistance is (or can be made) negligible over a considerable range of temperature.
.