## What is Electrical Resistance?

According to Ohm’s law, there is a relation between the current flowing through a conductor and the potential difference across it. It is given by,

V ∝ I

V = IR

**V**is the potential difference measured across the conductor (in volts)

**I**is the current through the conductor (in amperes)

**R**is the constant of proportionality called resistance (in ohms)

The electrical resistance of a circuit is defined as the ratio between the voltage applied to the current flowing through it. Rearranging the above relation,

R = \( \frac VI \)

The unit of electrical resistance is ohms.

1 ohm = \( \frac {1~ volt}{ 1 ~ampere}\)

### Electrical Resistance and Resistivity

So what is resistivity and how can we define resistivity? How is resistivity connected to electrical resistance?

### Factors Affecting Electrical Resistance

The electrical resistance of a conductor is dependent on the following factors:

- The cross-sectional area of the conductor
- Length of the conductor
- The material of the conductor
- The temperature of the conducting material

Electrical resistance is directly proportional to length (L) of the conductor and inversely proportional to the cross-sectional area (A). It is given by the following relation.

R = \( \frac{ρL}{A}\),

where ρ is the resistivity of the material (measured in Ωm, ohm meter)

Resistivity is a qualitative measurement of a material’s ability to resist flowing electric current. Obviously, insulators will have a higher value of resistivity than that of conductors. The resistivities of a few materials are given below for a comparison. Materials with a low value of resistivity conduct electricity very well.

- Silver – 1.00×10
^{−8} - Copper – 1.68×10
^{−8} - Aluminum – 2.82×10
^{−8} - Wood – 1.00×10
^{14} - Air – 2.30×10
^{16} - Teflon – 1.00×10
^{23}

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