a.    Effect of placing a soft iron core inside a solenoid:

• The strength and concentration of the magnetic field within the solenoid increases significantly.
• This occurs because soft iron is a ferromagnetic material with a high magnetic permeability, meaning it allows magnetic field lines to pass through it more easily than air.
• Ferromagnetic materials are made up of regions called magnetic domains. In an unmagnetised state, these domains are randomly oriented, so their individual magnetic fields cancel out.
• However, when a soft iron core is placed inside the solenoid, the external magnetic field produced by the current causes the domains to align with the field, creating a net magnetic field that reinforces the original one.
• Because soft iron is easily magnetised and demagnetised, it is ideal for use in electromagnets, where a strong, controllable, and reversible magnetic field is needed.

b.    Similarities:

• Field Pattern: Both produce magnetic fields with a similar dipole shape — field lines emerge from the north pole, curve around, and enter at the south pole, forming closed loops. Internally, the field lines run from south to north, creating a uniform field inside both the solenoid and the bar magnet.
• Effect on Magnetic Materials: Both fields can attract ferromagnetic materials (like iron) and influence their magnetic domains. A compass needle or small magnetic object placed near either field will align with the field lines.

Differences:

• Source of the Magnetic Field: A bar magnet’s field is generated by the alignment of permanent magnetic domains in the material. In contrast, a solenoid’s field is produced by electric current flowing through the wire coils, and can be turned on or off.
• Controllability: The magnetic field of a solenoid is adjustable, it can be increased by raising the current or number of turns and its direction reversed by changing current direction. A bar magnet’s field is fixed in strength and polarity unless the material is physically altered or demagnetised.