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Resistance

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Resistance is defined as the property of a substance due to which it opposes the flow of Electricity i.e electrons through it.


Metals, acids and salts are the good conductors of electricity.
These free or loosely attached electrons (vagrant) while flowing pass through the molecules or the atoms of the conductor,collide and other atoms and electrons, thereby producing heat.


The unit of Resistance
The practical unit of resistance is ohm. A conductor is have a resistance of one ohm if it permits one ampere current to flow through it when one volt is applied through its terminals.
The unit of resistance is ohm.

Laws of Resistance 
The resistance R offered by a conductor depends on the following factors:
1. It varies directly as its length l.
2. It varies inversely as the cross section A of the conductor.
3. It depends on the nature of the material.
4. It also depends on the temperature of the conductor.

R=ρ.l/A

where, ρ is a constant depending on the nature of the material of the conductor and is known as its specific resistance or resistivity.

Unit of resistivity:-
The unit of resistivity is ohm-m.


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