Question

A magnetic field lines due to a straight wire carrying current are
A. Straight
B. Circular
C. Parabolic
D. Elliptical

Answer 1

Hint: As we all know that magnetic field lines are one of the tools which are used to represent the magnetic field. They give information about the magnetic force on a north monopole at any position. Because monopole does not exist in nature. There is a strong connection between magnetic monopole and electric charges.

Complete step-by-step answer:
We can refer to below figure for proper understanding:

Here we can see the cylinder cross-section wire having a current I inside it and the magnetic field lines are in a plane perpendicular to the flow of current I.
 As we know that the magnetic field generated by the current. When we placed a compass near a long straight current-carrying wire exhibit field lines from circular loops centered on the wire. Also, the right-hand rule states that if the right-hand thumb points in the direction of the current, the fingers curl in the direction of the current.
Thus the magnetic field lines due to a straight wire carrying current are in circular form.

Therefore, the correct option is (B).

Additional information: We must keep in mind that magnetic field lines are imaginary lines. They exist in two types i.e. uniform and non –uniform magnetic field lines. Magnetic field lines are continuous and closed curved travelling from North to South Pole outside the magnet and south to North Pole inside the body of a magnet.

Note: We know that two magnetic field lines do not intersect each other because if they cross each other, then at the point of intersection, there will be the two directions of magnetic field at a single point, which is not possible. Widely spaced magnetic field lines represent weak magnetic fields and closely spaced field lines represent strong magnetic fields.