Question

If a soft iron is placed inside the current carrying conductor, what is the name given to the device?

Answer 1

Hint
Soft iron has a high magnetic permeability, in comparison with that of air. Therefore, it can get magnetized and demagnetized very easily. A current carrying conductor acts as a magnet, and when the soft iron is placed, the magnetic properties are improved.

Complete step by step answer
We know that the magnetic field inside a solenoid is given by, $B = {\mu _0}H$ where ${\mu _0}$ is the permeability of free space and $H$ is the magnetic field strength. Now, when the soft iron core is inserted, the dipoles in the iron align in the direction of the magnetic field of the solenoid. Therefore, the new magnetic field will be, ${B'} = {\mu _0}\left( {H + M} \right)$ where $M$ is the magnetization of the soft iron core.
Therefore, we find that when the soft iron core is inserted, the magnetic field inside the solenoid is enhanced. But, since the soft iron’s permeability is high, it gets demagnetized immediately on removing the current passing through the solenoid. These features are used in an electromagnet. When the soft iron core is inserted, the strength of the electromagnet is enhanced and the high permeability helps to get magnetized and demagnetized easily.
Hence it is clear that the device formed by a current carrying conductor inserted with a soft iron core is an electromagnet.

Note
Another benefit of placing a soft iron core is that there will be no permanent magnetism induced and that is essential for an electromagnet. However, there is a drawback in using the soft iron, that there will be increased hysteresis effects. That means, the increased current does not raise the magnetic field linearly, and therefore, the current supplied will not always give you the same magnetic field.