As we know that the resistance of the conductor are changes with change in temperature. So at the different temperature the resistance of the same conductor will be different.
The resistance increases as the temperature of a metallic conductor increase, so the resistance is directly proportional to the temperature. When we increases the temperature the amplitude of vibration of atoms increases as result of which the number of collision among the electrons and atom increases, and hence resistances increases.
The resistance remains Constance at any temperature. E.g. The resistance of eureka wire (60% cu, 40% nickle) is considered constant.
The resistance decreases as we increase the temperature of the liquid conductor. E.g. Battery has a liquid conductor (acid) in side it. In cool weather, the resistances of acid increase and hence the cars not start easily.
The resistance of cu, Ni, manganese material are normally high resistance at low temperature. But when the temperature increases so the resistance of the material decreases. These materials are used in the circuit for voltage regulation.
TEMPERATURE CO-EFFICIENT OF A RESISTANCE
temperature co-efficient of a resistance is the amount by which resistance changes when temperature changes per degree centigrade. It is represented by alpha α.
When we increase the temperature as a result the resistance increase so the temperature of that materials are called positive temperature co-efficient and hence when we increase the temperature and the resistance decrease so the temperature of that materials are called —ve temperature coefficient. Suppose the resistance of a conductor at 0o C is R0 Ω increasing the temperature to C, the resistance becomes Rt Ω, as shown in fig.
Change in resistance =ΔR
ΔR = Rt - Ro
ΔR depends upon the fallowing three factors.
1. ΔR is directly proportional to the initial resistance, Ro
ΔR α Ro
2. ΔR is directly proportional to the rise in temperature, t0C
ΔR α to C
3. ΔR depend upon the nature of conductor.
According to factor (1) and (2), we can write
ΔR α Ro .........................(1)
ΔR α to C .........................(2)
Compare eq (1) and (2)
Where (α) is called temperature co-efficient of resistances. From eq we can find
It is the increase in resistance per ohm original resistance per °c rise in temperature is called temperature co-efficient.