Explain Unit of Specific Resistance - QS Study

Electrical resistivity (also known as resistivity, specific electrical resistance, or volume resistivity) is an intrinsic property that quantifies how strongly a given material opposes the flow of electric current.

In equation R = ρ (L/A) we can write, ρ = R (A/L)

Substituting the units of the quantities on the right side of the equation, the unit of ρ is:

Ωm2/m = Ωm

Significance: The resistivity of silver at 20 °C is 1.6 x 10-8 Ωm. Therefore, the resistance of a silver wire of length l m and cross sectional area of 1m2 is 1.6 x 10-8. Table shows the values of the resistivity of some common materials.

Table: Resistivities of different materials

From the table above we see that the materials with lower resistivities are good conductors of electricity. For example- copper is much better conductor of electricity than nichrome. Due to this, copper is widely used as connecting wires in electrical circuits.

Besides, materials with higher resistivities also have multiple uses. One example is the nichrome wire. The resistivity and melting point of nichrome is much higher than that of copper. Due to the high resistivity of nichrome, a lot of thermal energy is produced when a current flows through it. This property of nichrome causes water to boil very quickly in electric kettle. The filament of electric bulbs that are used in our houses is made of tungsten. Tungsten can convert electrical energy to light and thermal energy owing to its high resistivity and melting point.