# Soft iron core

I would like to know what is the function of soft iron core?
Is there a difference in function when inserting soft iron core in inductor , motor , generator ?
Thank you

$$B=\mu_r\mu_\circ{N\cdot I\over L}$$
Here $$\mu_\circ=4\pi10^{-7}$$ is the permeability of vacuum.
$$\mu_r$$ is the permeability of the core of the coil. If the core is just air, $$\mu_r=1$$, and you obtain the same B as in the vacuum. For almost all substances $$\mu_r \simeq 1$$. But for ferromagnetic ones (iron, nickel, cobalt, and a few more), $$\mu_r$$ can be very big, 10 000 or even 50 000. You get a magnetic field ten thousand times bigger!