**Resistance of Conductor-**

**We know-**

- When a potential difference is applied across the two ends of a conductor, an electric field is established inside it.
- The electric field exerts an electric force on the free electrons and they start drifting in the direction opposite to electric field.

The property of a conductor by virtue of which it opposes the flow of charges through it is called as its resistance. |

Any material that has a property of offering resistance is called as a **resistor**.

**Cause of Resistance-**

- When electrons drift inside the conductor, they frequently collide with the positive metal ions.
- The
**collisions of free electrons**with the positive metal ions is the main cause of resistance of the conductor.

**Calculation of Resistance-**

**The resistance of a conductor is equal to the ratio of the potential difference applied across the conductor to the current flowing through it.**

**SI Unit of Resistance-**

- The SI unit of resistance is
**ohm (Ω)**. - The resistance of a conductor is said to be
**one ohm**if a current of 1 A flows through it when a potential difference of 1 V is applied across its ends.

**Factors Affecting The Resistance-**

The resistance of a conductor depends upon the following factors-

**1. Length of Conductor-**

- The resistance of a conductor increases with the increase in its length.
- Thus, resistance of a conductor is directly proportional to its length i.e.

**R ∝ L**

**2. Cross-sectional area of Conductor-**

- The resistance of a conductor decreases with the increase in its cross-sectional area.
- Thus, resistance of a conductor is inversely proportional to its cross-sectional area i.e.

**R ∝ 1/A**

**3. Nature of material of Conductor-**

- The resistance of a conductor also depends upon nature of material of the conductor.
**For example-**the resistance of nichrome wire is 60 times that of a copper wire of same length and same area of cross-section.

**4. Temperature of Conductor-**

- The resistance of a conductor increases with the increase in its temperature.
- With the rise in temperature, the
**drift velocity**of electrons increases and hence they collide more frequently with each other. - Due to increased collisions, the resistance of conductor also increases.

**At a constant temperature, on combining the above factors, we get-**

**OR**

Here, ρ is a constant of proportionality called as **resistivity** or **specific resistance** of the material of the conductor.

**Conductance of Conductor-**

The conductance of a conductor is the ease with which electric charges flow through it. |

- More is the resistance of a conductor, lesser is its conductance and vice-versa.
- So, conductance of a conductor is defined as reciprocal of resistance of the conductor.
- It is denoted by G.

**Mathematically,**

**OR**

The SI unit of conductance is **ohm ^{-1}** or

**mho**or

**siemens (S)**.

**Read the next article on-**

**Resistivity & Conductivity of Conductor**

**Get more notes & other study material of the Chapter** **Current Electricity**.