Resistance: Resistance of a conductor is the opposition offered by the conductor to the flow of current through it.
Resistances are of two type fixed resistance and variable resistance.
Reason of resistance: The resistance is due to collision of moving electrons while moving from negative terminal to positive terminal. In this process when electrons collide with positive ions , few electrons drift away and do not reach to the positive terminal. Because of this drifted electrons the conductance of the conductor decreases and therefore resistance results in this process.Conductance = 1 / resistance
Rt=R0 ( 1+ α t) ohm.
where t = Tt - T 0
Where Rt = Resistance at temperature t 0C
R0 = Resistance at temperature 00C
α = temperature Co-efficient of resistance of a particular conductor.
|Temperature Co-efficients (α)|
|Conductor Material||Temp. Co-efficent||Unit||Copper||4.041 x 10-3||Ohm-m|
|Aluminium||4.308 x 10-3||Ohm-m|
Resistance formula from the relation of potential difference and current is given below.
Resistance = Potential difference / Current
R = V / I VA-1
This unit VA-1 is named as Ohm.
From the power equation we can write the resistance formula as
R = W / I2