Resistance and resistivity difference
|It is the opposition to the flow of electric current through a conductor.||It is the resistance of a meter cube of a wire.|
|Its SI unit is ohm ( Ω ).||Its SI unit is ohm-meter (Ω-m).|
|It depends upon the length and area of cross section of wire.||It does not depend upon the length and area of cross section of wire.|
We learn in detail about resistance and resistivity.
From the relation of Ohm’s law (V=IR),R is the constant of proportionality and is called the resistance of the conductor.It is defined as:”The opposition to the flow of charge through a conductor is called electrical resistance.
The SI unit of resistance is ohm (Ω ).It is defined as “Resistance is said to be 1 ohm, when one ampere of current passes through the conductor due to the potential difference of one volt across its ends.”It can be expressed as:
R = V/I
1 ohm =1 volt/1 ampere
The resistance of a conductor depends upon
- Dimensions of the conductor ( length and area of the cross-section).
- The physical state of the conductor (temperature etc ).
What is resistivity?
Resistivity can be defined as the resistance of a meter cube of a wire.It is the property of the material of which the wire is made.
It has been observed experimentally that the resistance R of a wire is directly proportional to its length L and inversely proportional to its area of cross section of the wire.i.e
If L= 1m and A= 1m² ,then above equation (3) becomes ρ = R.
So resistivity is defined as: ” the resistance of wire whose length is one meter and whose area of cross-section is one-meter square.
SI unit of resistivity is ohm-meter (Ωm).It depends upon nature of material and temperature of the material,it is independent of dimensions of the conductor.
The resistivity of some materials is given in the table:
Effect of temperature on resistance
The resistance and resistivity of a substance depend upon the temperature.As the temperature of the conductor rises, the amplitude of vibration of the atoms in the lattice increases.So, the collision cross section of the atoms increases.
Thus the atoms then offer a bigger target.This increases the probability of their collision with free electrons.Hence, the resistance of conductor increases.
Experimentally, it is found that changes in resistivity of a metallic conductor with the temperature are linear over a considerable range below and above 0 Cº.This shows that resistivity is not zero at 0 Cº.
Temperature coefficient of resistance
The fractional change in resistance of a substance per kelvin is called temperature coefficient of resistance.
Mathematically it is expressed as:
R0= Resistance of material at 0 Cº.
Rt = Resistance of material at t Cº.
t = Change in temperature
α = temperature coefficient of resistance.
Temperature coefficient of resistivity
The fractional change in resistivity of material per kelvin is called temperature coefficient of resistivity.Mathematically it is expressed as:
ρ0= Resistivity of material at 0 Cº.
ρt = Resistivity of material at t Cº.
t = Change in temperature
α = temperature coefficient of Resistivity.
SI unit of the temperature coefficient of resistance /resistivity is per kelvin.
Lets see video about the difference between resistance and resistivity.