Question

Define electric resistance of a conductor.

Answer 1

A conductor is a substance that conducts electricity. However, in every conductor there is an opposition to the current or flow of charges. This ability of the conductor to oppose the flow of charges is called resistance.

Complete answer:
We know that when a charge is placed in between a potential difference, the charge accelerates. A potential difference produced an electric field. The electric field exerts a force on the charge and therefore the charge accelerates.

A conductor consists of electrons. An electron has a charge of –e. Therefore, when a potential difference is created by attaching a cell across the given conductor, the electrons are accelerated under the influence of the electric field. Hence, there is a flow of charge in the circuit.

However, the charges (electrons) do not flow easily. They do not accelerate and a flow with a constant velocity called drift velocity. This is due to many factors such as the collisions between the electrons and some properties of the material of the conductor.

Therefore, we say that the material of the conductor opposes the flow of the charges. This property of the material is called the resistivity of the material.
Conductors of different sizes but the same material have the same value of resistivity. However, the ability to oppose the flow of charges depends on the dimensions of the conductor too. Hence, we define the resistance of the conductor.

Resistance of a conductor is the ability of a conductor of defined length and cross sectional area to oppose the flow of charges (electrons).

Suppose a conductor has a length L and a uniform cross sectional area A. If the resistivity of the material of the conductor is $\rho$ then the resistance of this conductor is given as $R=\rho \dfrac{L}{A}$.
Hence, we can also say that the resistance of a conductor is equal to the resistivity of its material when the length and cross sectional area of the conductor are one unit each.

Note:
(i) Do not confuse between resistance and specific resistance.
Specific resistance is equal to the resistivity of the material.
Resistance depends on the dimensions of the material whereas resistivity is independent of the dimensions of the material.
(ii) According to Ohm’s law, V = iR. Here, V is the potential difference created across the conductor and i is the current flowing through the conductor.
Hence, $R=\dfrac{V}{i}$.
Therefore, we can also define resistance as the potential difference that has to be created across the conductor so that the current flowing through the conductor is one unit.