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Laws of Resistance and Specific Resistance

Laws of Resistance and Specific Resistance
The laws of resistance states that the Resistance “R” offered by a conductor depends upon following factors:

1. The Resistance “R” is directly proportional with it’s length “L”

2. The Resistance “R” is Inversely proportional with it’s Cross Sectional Area: “A”


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3. The Resistance “R” is dependent on the Nature of the material.

4. The Resistance “R” is dependent on the Temperature of the conductor.

Note:- It is found that among physical factors Temperature plays the most significant factor in determining the resistance but other physical factors like Pressure and Tension also effect the resistance of a substance.

Resistivity or Specific Resistance:


If we do not change the temperature of the conductor or neglect it’s effect then we can come into conclusion that:

The resistance of a substance is directly proportional to it’ length divided by it’s cross sectional area.

Or,         

or,               ,


where is a constant depending on the nature of the material of 
the conductor and is known as it’s Specific Resistance or Resistivity.

When L = 1 Meter and A = 1 Meter square Or when the material takes in of length 1 meter and it’s cross sectional area is one meter square as shown on the figure below then ,

So the specific resistance of a substance can be defined as the resistance between the opposite faces of a meter cube of that material.

Formula and Unit of Specific Resistance:
From the equations derived above we can derive the formula for resistivity.So , the unit of resistivity is : Ohm Meters

1 comment:

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