Question

When there is an electric current flowing through a conducting wire along its length then an electric field must exist
A. Inside the wire but normal to it
B. Inside the wire but parallel to it
C. Outside the wire but normal to it
D. Outside the wire but parallel to it

Answer 1

Hint: When we speak of electric current, we mean the rate of flow of charges. An electric conductor conducts electricity only when the electric field exists inside the conductor. The electric field exists at the place where current flows. The flow of charges requires a medium in which it can flow. Use these basics to find when there is an electric current flowing through a conducting wire where the electric field exists.

Complete step by step answer:
It is given that the electric current is flowing through the conducting wire along its length. As the current flows along the lengths of the wire, charges also flow along its length. So, there must be some electric field parallel to the length of the wire. As the charges are moving inside, the electric field will also be inside the wire. Thus, for a current carrying conductor, electric field inside the metal and the magnetic field outside the wire.
Therefore, when an electric current is passed through a conducting wire along its length, the electric field exists inside the wire but parallel to it.

So, the correct answer is option B i.e. inside the wire but parallel to it.

Note:
Electric fields can exist outside the wire if the thickness of the conducting wire varies along the line then the field exists outside. Also, if the wire is not straight and bends at some point then the electric field will exist outside the wire or if the current varies with time then too the field will be outside the wire. Students must know that a large current moves large amounts of charges in small amounts of time. Whereas a small current moves a small amount of charges in a long time.