**Resistivity Formula**

Resistivity, denoted by the Greek letter rho(p), is defined as the resistance R of a specimen, such as a wire, multiplied by the cross-sectional area A and divided by the length l; ρ= RA/L. Its unit is the ohm(Ω).

Electrical resistivity refers to the resistance of a material’s current flow from one end to the other. Electrical resistivity is a straightforward and informative metric for describing a substance. It is the inverse of electrical conductivity.

The resistivity is denoted by and is proportional to both the material resistance and the length. The area of cross-section of a given material is inversely related to its resistivity.

The ratio of the area in square metres to length in metres is simplified to merely metres in the metre-kilogram-second (mks) method. The unit of resistivity in the metre-kilogram-second system is therefore ohm-metre. Resistivity can be stated in ohm-centimetre units if lengths are measured in centimetres.

The resistivities of electrical insulators range from 1012 to 1020 ohm-metres.

**Formula:**

The resistivity formula is as follows:

Formula for Resistivity : ρ = RA/l

Where ρ denotes resistivity, R denotes resistance, l denotes material length, and A denotes cross-sectional area.

**Solved Examples**

**1. Calculate the resistivity of a material with a resistance of 3Ω and a cross-sectional area and length of 25 cm2 and 10 cm, respectively.**

**Solution:**

Given

R = 3 Ω

l = 10 cm = 0.10 m

A = 25 cm2 = 0.25 m2

Resistivity is:

ρ = RA / l

ρ = (3 × 0.25) / 0.10

ρ = 7.5 Ωm

**2. The wire’s length and area are 0.3 m and 1.0 m2, respectively. Calculate the resistivity of that wire if its resistance is 5Ω.**

**Solution:**

Given

R = 5 Ω

l = 0.3 m and

A = 1.0 m2

Resistivity is:

ρ = RA / l

ρ = (5 × 1) / 0.3

ρ = 16.66 Ωm