# 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”

Related Links:

Types of Resistors

Resistors Colour Coding

Multimeter: Testing Resistors

Effect of temperature on Resistance Of Materials

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

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

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.

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”

Related Links:

Types of Resistors

Resistors Colour Coding

Multimeter: Testing Resistors

Effect of temperature on Resistance Of Materials

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: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 ,

__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
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