Question

The magnetic field lines inside a long, current-carrying solenoid are near;
A. Straight
B. Circular
C. Parabolic
D. Elliptical

Answer 1

Solenoid is an electromagnet that is used to produce a controlled magnetic field through the coil. The insulated wires are wrapped around an iron or other ferromagnetic material cylinder, this arrangement is called a solenoid.

Complete step by step solution:
When current passes through the wires, a magnetic field is produced. Solenoid behaves like a permanent bar magnet. Whose south and north poles are the ends from where magnetic field lines are coming in and out, respectively. There are two types of solenoid: finite and infinite solenoid. A finite solenoid is the one whose length is finite and the infinite is the one whose length is infinite such that the end effects are negligible.
The magnetic field lines are parallel to the axis of the long infinite solenoid and the magnetic field does not vary along the length. The magnetic field almost seems to be a straight line.
Hence, the correct option is (A) straight.

Note:
Solenoid converts electrical energy into mechanical work, it is a device that creates a magnetic field using electric current.
The magnetic field outside the solenoid is zero. Magnetic field lines are in the form of a loop, they neither diverge or converge like electric field lines. So, in a solenoid, magnetic field lines follow the longitudinal path along the length of the solenoid and form a loop.
The magnetic field inside the infinitely long solenoid is constant. Its strength does not depend on the area of cross-section and distance from the axis of the solenoid.