Resistance

Resistance is the opposition to the flow of electric current offered by a substance. In simple words, atoms and molecules of a substance obstruct the flow of free electrons. The amount of opposition, or resistance, applied against the electric current depends on the nature of the substance. Metals like silver, copper, aluminium offer very little resistance to the electric current. Hence, they are called conductors. Some substances, on the other hand, provide high amount of resistance to the flow of electric current. They are called insulators. Glass, rubber, dry wood, mica are some examples of insulators. Metals like silver, copper, aluminium offer very little resistance to the electric current. Hence, they are called conductors. Some substances, on the other hand, provide high amount of resistance to the flow of electric current. They are called insulators. Glass, rubber, dry wood, mica are some examples of insulators.

The resistance of a conductor depends upon:

•          the length of the conductor; to which it is directly proportional;

•          its area of cross-section, to which it is inversely proportional;

•          nature of the material;

•          temperature.

Symbol:

                  Resistance: R µ l/a
                  R = p l/a

Where is constant and is known as resistivity or specific resistance.

Measurement: The unit of measurement for resistance is ohm (Ω).

Resistance can be measured by using an ohmmeter in Ω, a multimeter in kΩ and a megger in m Ω.