Question

A uniform magnetic field parallel to the plane of paper, existed in space initially directed from left to right. When a bar of soft iron is placed in the field parallel to it, the lines of force passing through it will be represented by a figure.
A.
B.
C.
D.

Answer 1

Hint: In this question we will use the concept of permeability of ferromagnetic materials. When in proximity to a magnetic field, the atoms of ferromagnetic material start to align their electrons with the flow of the magnetic field. It becomes magnetised as a result of the magnetic field. Consequently, an attraction develops between the two. For this reason, an iron object that is for some time becomes magnetic when exposed to a magnet.

Complete step by step solution:
Soft iron has maximum permeability relative to other metals. Therefore, as a significant magnetization arises in the direction of the field in the ferromagnetic material, the maximum lines of force tend to travel through the soft iron.

Hence, the correct answer is B.

Additional Information: Permeability is the amount of magnetization that a material acquires in electromagnetism in response to an applied magnetic field. The (italicised) Greek letter is commonly used to denote permeability. Magnetic reluctivity is permeability's inverse.

Henries per metre (H/m), or Newtons per Ampere Squared ($N/A^2$) are the SI units used to express permeability. The proportionality between magnetic induction and magnetising force when producing a magnetic field in a classical vacuum is known as the permeability constant 0, commonly referred to as the magnetic constant or the permeability of free space.

Note: Because the internal molecular structure of iron is easily able to create these magnetic field lines, iron provides a low reluctance channel and aids in the creation of magnetic fields, which is referred to as "High Permeability."