Soft iron core is used in dynamo or generator because it helps to induce more current in the circuits.
A soft iron core is used in a moving coil galvanometer. The soft iron core attracts the magnetic lines of force and hence the strength of the magnetic field increases if we use soft iron core. Thus the sensitivity of galvanometer increases.
Soft iron core is used in electromagnets because they get easily magnetised/demagnetised when current is flowing or not flowing along the solenoid. Whereas, steel is a permanent magnet and does not lose it's magnetization even when the current is switched off. Hence, soft iron core is preferred over steel core.Soft iron is used because it does not retain its magnetism when the current is switched off; in other words, it does not become permanently magnetized.
Soft iron is iron that has low carbon content and is easily magnetized and demagnetized. It is used to make the cores of solenoids and other electrical equipments. ... In other words, the magnetic domains of hard iron do return to the starting point when magnetic field is removed.It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites. The high permeability, relative to the surrounding air, causes the magnetic field lines to be concentrated in the core material. The magnetic field is often created by a current-carrying coil of wire around the core.