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