Question

Across a metallic conductor of non-uniform cross section a constant potential difference is applied. The quantity which remains constant along the conductor is:
(A) Drift velocity
(B) Electric field
(C) Current density
(D) Current

Answer 1

Hint: We will find the quantity which is unaffected by the non-uniformity of the metallic conductor. In the above condition, rate of flow of charge is always maintained and it is unaffected.

Complete step by step answer:
In the given question, we are supplied the following data:
The potential difference applied across the metallic conductor is non-uniform in nature.The cross section of the metallic conductor is non-uniform.We are asked to find among drift velocity, electric field, current density and current, which of the following quantities will remain constant.
Let’s find out what the above physical quantities mean anyway.
Current: It is defined as the amount of charge which is passing through a given point in a given time. Precisely, we can say that the rate of flow of charge is called current. Its unit is amperes. It does not depend on the physical characteristics of the medium or material. Whatever be the material is, if it is conducting in nature then charge will definitely flow through it.
Drift velocity: The average velocity achieved by charged particles, such as electrons, in a material due to an electric field is drift velocity. In general, at Fermi velocity, an electron in a conductor will spread spontaneously, resulting in an average velocity of zero. Applying an electric field applies a slight net flow in one direction to this random motion; this is the drift.
Electric field: It is the force which is defined as the electric force per unit charge. It depends upon the charge produced by the electric field and the separation of the test charge and the electric field.
Current density: It is the amount of charge passing through a unit area per unit time. But if the material is non-uniform in nature, then the current density will not be uniform.Hence, from the above explanation it is clear that the current is not affected when a constant potential difference is applied across a non-uniform metallic conductor.
The correct option is D.

Note: In this question we are asked to find the physical quantity which remains unaffected. Current just depends on the potential difference applied across a conductor. However, flow of current is affected by the presence of resistance in it. Higher the resistance in it, lesser is the current flow or vice-versa.