The magnetic field inside a solenoid is:

Explanation:

The Magnetic Field Inside a Solenoid

Definition: A solenoid is a coil of wire that is wound in a helical shape, and when an electric current is passed through it, a magnetic field is generated. The magnetic field inside a solenoid is a result of the superposition of the fields created by each turn of the wire, leading to a strong and uniform magnetic field along the axis of the solenoid.

The solenoid operates on the principle of electromagnetism. When an electric current flows through the coil, it creates a magnetic field. According to Ampère's circuital law, the magnetic field inside a solenoid is given by:

B = μ₀ * n * I

where B is the magnetic field, μ₀ is the permeability of free space, n is the number of turns per unit length of the solenoid, and I is the current flowing through the solenoid. This equation highlights that the magnetic field inside a solenoid depends directly on the current and the number of turns per unit length.

Uniform and Parallel Magnetic Field: The correct option, which is option 3, indicates that the magnetic field inside a solenoid is uniform and parallel. This is because the field lines inside a long solenoid are parallel to its axis and are evenly spaced, implying uniform strength. This uniformity is due to the symmetry and the consistent current flow through the turns of the coil.