» Resistance (Symbol R):
Its ability to oppose the flow of charge through it. In general, the resistance is the ratio of the potential difference across an electrical component to the current passing it.
Mathematically,
$R = \frac{V}{I}$ .......... (i)
Where, V = Voltage and I = Current. It's unit is ohm $(\Omega)$ in SI unit.
The one ohm $(1 \; \Omega)$ of the conductor is defined as, if one ampere current flows through the resistance under a potential difference of one volt. i.e.
$1\; \Omega = \frac{1\; Volt}{1\; Ampere}$ .......... (ii)
Click here for the Resistance Colors code
» Resistivity (Symbol $\rho$):
The electrical resistivity of a conductor (material) is a measure of how strongly the material opposes the flow of electric current through it. The resistivity is depends upon the lengths and cross-sectional areas of the conductor. The higher the resistivity $\rho$ the more the resistance and vice-versa.
For example: The resistivity of a copper (good conductor) is in the order of 1.72 * 10$^-8$ Ω m. Whereas the resistivity of a air (insulator / poor conductor) 10$^{10}$ 10 $^{14}$ Ω m.
The resistivity of a conductor s defined as the resistance of the conductor of unit cross-sectional area per unit length. It's unit is ohm meter (Ω m), in SI system.
$\rho = R\frac{A}{l}$ .......... (iii)
Mathematically,
Let length $l$ of the conductor having resistance $R$ and its cross sectional area $A$.
At constant temperature,
The resistance $R$ of the conductor is directly proportional to the length $l$ of the conductor.
$R ∝ l$ .......... (iv)
And, the resistance $R$ of the conductor is inversely proportional to the cross sectional area $A$.
$R ∝ \frac{1}{A}$ .......... (v)
From equation (iv) and (v), we get
$R ∝ \frac{l}{A}$
or, $R = \rho \frac{l}{A}$ .......... (vi)
Where $\rho$ is a proportionality constant called 'Resistivity of a conductor'.
Return to Main Menu