Which one of the following statements regarding a current-carrying solenoid is not correct?

A current-carrying solenoid generates a magnetic field that is uniform and strong inside the coil, with field lines running parallel to the axis [1]. It behaves like a bar magnet, exhibiting distinct north and south poles [2]. The magnetic field strength (B) is directly proportional to the current (I) flowing through it, as defined by the relation B = μ₀nI; thus, increasing the current increases the field strength [1]. However, statement 4 is incorrect because inserting a soft iron bar significantly increases the magnetic field strength [1]. Soft iron has high magnetic permeability, which concentrates the magnetic flux and magnetizes the core, transforming the solenoid into a much stronger electromagnet [2]. Therefore, the claim that the magnetic field remains the same is false.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > 12.2.4 Magnetic Field due to a Current in a Solenoid > p. 201
2. [2] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > What you have learnt > p. 206