Effect Of Temperature On Resistance

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.

METALLIC CONDUCTOR

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.

ALLOY

The resistance remains Constance at any temperature. E.g. The resistance of eureka wire (60% cu, 40% nickle) is considered constant.

LIQUID CONDUCTOR

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.

THERMISTOR MATERIAL

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 0^o C is R0 Ω increasing the temperature t^o 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 t^o C

3. ΔR depend upon the nature of conductor.

According to factor (1) and (2), we can write

ΔR α R_O    .........................(1)
ΔR α t^o C  .........................(2)

Compare eq (1) and (2)

Where (α) is called temperature co-efficient of resistances. From equation we can find

It is the increase in resistance per ohm original resistance per °c rise in temperature is called temperature co-efficient.