As per the previous discussion,
Resistance R = ρ(l/A)
Where,
l : Length
of the conductor
A : Cross-sectional
area of the conductor.
Through this equation it can be said that resistance is directly proportional
to the length and is inversely proportional to the cross-sectional area of the
conductor.
But it also depends on the temperature which is often neglected.
The electron movement across a conductor is often obstructed by
the atoms and molecules present in the conductor. With the increase in
temperature the atoms and molecules present bounce around making the movement
of electrons harder. Which directly corresponds to the increase in the
resistance.
For small temperature changes the resistivity of the conductor is
linear to temperature as follows;
Where,
r : Final Resistivity
ro : Initial
Resistivity
a : Temperature co-efficient of
resistivity
DT : Temperature change
Assuming that the length and the cross-sectional area does not
change with the temperature change,we often use the formula,
R = Ro (1 + a DT)
Where,
R : Final Resistance
Ro : Initial
Resistance
a : Temperature co-efficient of
resistivity
DT : Temperature change
In some materials like silicon the temperature co-efficient of
resisticity is negative which means that the resistance reduces with the
temperature, in those materials increase in the temperature can make the
charges move freely thus increase the current movement.
This
αo is known as the temperature coefficient of resistance of a
substance at 0 degree Celsius.
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