Question

Which of the following statements is correct about the magnetic lines of force inside a current-carrying solenoid?
A) Magnetic field lines are along the axis and parallel to each other.
B) Magnetic field lines are perpendicular and equidistant from each other.
C) Magnetic field lines are circular and do not intersect each other.
D) Magnetic field lines are circular at the end but are parallel to the axis inside the solenoid.

Answer 1

A an insulated copper wire bent in the form of a coil having many circular turns, which is wrapped closely to form a cylindrical shape is considered as a solenoid. The magnetic field inside the solenoid is uniform but outside the solenoid, the magnetic field varies.

Complete step by step solution:
Step 1: Based on the strength of the magnetic field inside and outside the solenoid, we can sketch the magnetic lines of force.

It is a known fact that the magnetic field inside a solenoid is uniform. This means that the strength of the magnetic field is constant at all points in the interior of the current-carrying solenoid. This uniformity of the magnetic field strength can be indicated by lines of force drawn parallel to the axis of the solenoid.

Since the magnetic field lines form a closed loop, the field lines near to ends of the solenoid will be circular.

So we can conclude that the magnetic field lines inside the solenoid are parallel to the axis of the solenoid but near to the ends of the solenoid, they will be circular. The figure given below depicts the field lines for the current-carrying solenoid.

So the correct option is D.

Note: The magnetic field lines in the above-sketched figure resembles the field lines of a bar magnet.
The below figure depicts the field lines of a bar magnet.

So we can also conclude that the current-carrying solenoid is like a bar magnet. One end of the solenoid will behave like a magnetic north pole from where the field lines start and its other end will behave like a magnetic south pole where the field lines end. The net magnetic field outside the solenoid is zero and the field lines will not intersect each other.