Question

The best material for the core of a transformer is:
A. Mild steel
B. Stainless steel
C. Soft iron
D. Hard steel

Answer 1

Hint: The best material used for the core of a transformer must be a material which allows the passage of magnetic lines of flux easily. If all the lines of flux produced within the transformer are linked with the core, the energy losses are minimum and hence the E.M.F generated is maximum.

Complete step by step answer:
First of all before understanding the logic behind the linking of flux, we have to understand what is permeability of a material?
Now, permeability of a material is the measure of resistance offered by a material towards the ease of formation of the magnetic field inside it. High permeability of a material means the material can conduct the magnetic lines of flux easily. Where-as a material with lower permeability will resist the formation of a magnetic field inside it.
High permeable material helps the flux to pass through them easily and hence the flux density in the region (air) around the core becomes very low. Due to this reason, the flux linked with the coil increases and hence eventually, the E.M.F induced in the transformer increases.
Hence it is highly advised to use a material with higher permeability to use in core.
Now, among all of the above mentioned materials, permeability of soft iron is the maximum and hence is used in transformers. Thus option C. is correct.
Soft iron: It is a kind of iron having lower iron content due to which it is easy to magnetize and demagnetize it. Hence it serves as an advantage of using it in transformers.

Note:
The measurement of permeability usually is not done by direct values. We define a term called relative permeability of the material which is the ratio of permeability of the material to that of free space (vacuum). For soft iron, relative permeability of iron is 200,000. Which means it is 200,000 times easier for the flux to pass through it rather than through free space.