Mechanism of Current Flow In A Conductor-

 

Before you go through this article, make sure that you have gone through the previous article on Mechanism of Current Flow In A Conductor.

 

We have learnt-

• When a potential difference is applied across the ends of a conductor, an electric field is created inside it.
• The electric field applies an electric force on the free electrons inside the conductor.
• As a result, they start drifting in a preferred direction and the flow of current starts.

 

In this article, we will learn about resistance & conductance of a conductor.

 

Resistance of Conductor-

 

The resistance of a conductor is defined as-

 

The property of a conductor by virtue of which it opposes the flow of charge carriers 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 free 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 potential difference applied across the conductor to the current flowing through it.

 

Mathematically,

 

 

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 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 on the 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 collisions of free electrons with the other free electrons and with the positive metal ions increases.
• 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 charge carriers can 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 the reciprocal of resistance of the conductor.
• It is denoted by the symbol G.

 

Mathematically,

 

OR

 

The SI unit of conductance is ohm^-1 or mho or siemens (S).

 

Test Your Concepts-

Quiz on Resistance & Conductance

 

Next Article-

Temperature Dependence of Resistance

 

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