Question

Soft iron is preferred as the core of transformers due to its :
A. low coercivity and low retentivity
B. low coercivity and high retentivity
C. high coercivity and high retentivity
D. high coercivity and low retentivity

Answer 1

Hint: The capacity of a ferromagnetic material to tolerate an external magnetic field without getting demagnetized is measured by coercivity, also known as magnetic coercivity, coercive field, or coercive force. Electric coercivity, an equivalent quality in electrical engineering and materials science, is a ferroelectric material's capacity to tolerate an external electric field without becoming depolarized.

Complete answer:
In transformers, soft iron cores are utilised because they have excellent magnetic permeability, which focuses magnetic lines of force and reduces energy loss. Because soft iron has a high permeability, it allows full coupling of magnetic flux from the main coil to the secondary coil in the core of a transformer. It has a high coercivity and a low retentivity as a result. A solenoid is the simplest motion generator, consisting of a coil with a soft iron core (or armature) that glides easily in and out of the coil. Soft iron is utilised because it does not lose its magnetic field when the current is turned off; in other words, it does not get magnetised permanently.
The transformer core offers a magnetic route via which flux can be channelled. Improved core building procedures, as well as the use of highly permeable material (which characterises the material's capacity to transmit flux), assist in producing a desired, low reluctance flux route and restrict lines of flux to the core. Low stray magnetic fields in Iron Core Coils help solve a variety of difficulties. When stray magnetic fields are strong enough, they can disrupt adjacent power systems and cause eddy currents in steel. A transformer core is a static device that uses electromagnetic induction to transport electricity from one source to another.
These are bits of magnetic material with a high magnetic permeability that are used in transformers to direct magnetic fields. Because soft iron has a high permeability, it allows full coupling of magnetic flux from the main coil to the secondary coil in the core of a transformer. It has a high coercivity and a low retentivity as a result. Because of its high permeability$$\mu$$, soft iron is the optimum material for a transformer's core. It has a short hysteresis curve and has a very low coercivity.

Hence option d is correct.

Note:
When an external magnetic field is removed from a ferromagnetic substance (such as iron), remanence is the magnetization that remains. When a magnet is "magnetised," it is said to have remanence. Magnetic materials' remanence offers magnetic memory in magnetic storage devices and is utilised in paleomagnetism as a source of knowledge on the past Earth's magnetic field. The term remanence comes from the words remnant and -ence, which means "something which stays." Remanence measured in magnetic flux density units is also referred to as retentivity.