Answer:
It is used to increase the magnetic field intensity produce by the electromagnet
Step-by-step explanation:
As we know that the magnetic field produced by the electromagnet is given by the formula

here we know that
= permeability of the free space
n = number of turns per unit length
i = electric current
so here we can say that if the permeability of medium is increased then the intensity of magnetic field will also increase
So we can use metal core to increase the field intensity produced by electromagnet