Answer: The metal core helps to amplify the magnetic field created by the coil of the electromagnet.
Explanation: Electromagnet uses coil of wire, as current flows through the coil, the magnetic field generated by each loop adds to the field generated by the other loops, producing a definitive “north” and “south” (or positive and negative) end and this leads to magnetism. Addition of a core would improve the magnetism of the electromagnet. The core is a magnetic material that the wire is wrapped around. Therefore, the field produced by the coil aligns with the magnetic domains in the material, so both the coil and the physical magnetic core work together to produce a stronger field than either could produce alone.
The metal core mostly used in an electromagnet is an iron core because of its higher relative permeability to magnetic fields compared to other metals.