# Physics Assignment Help With Resistance

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## 12.6 Resistance

Resistance is the property of a substance by which it opposes the flow of current through it.

For a given body, the resistance is defined as the ratio of applied potential difference to the resulting current, *R* =

This property of the substance is due to frequent collisions of electrons with the atoms of the conductor.

SI unit of resistance is named ohm ) which is equivalent to V/A. Its dimensions areW(

[*R*] = .

### 12.6.1 Dependence of Resistance on Physical Dimensions

For a given body, its resistance is found to be

- directly proportional to its length (
*L*), and - inversely proportional to its area of cross-section (
*S*).

That is, *R* µ *L* and *R* µ

or *R* µ = r

where r is a constant called *resistivity*.

### 12.6.2 Resistivity or Specific Resistance (r)

The constant r is the characteristic of the material depends on its temperature of which the conductor is made. If *L *= unity and *S* = unity, then *R *= r

It can also be defined as the resistance of a cube of material of side 1 m when current flows perpendicular to opposite faces.

The SI unit of resistivity is ohm metre (W m).

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