Transformer: Why stack the core?

 The design of the magnetic core does not allow any current to flow. However, it is a conductive loop that undergoes a changing magnetic field, so small currents are induced in it-these are called "eddy currents."

Laminated cores reduce it to a minimum because they interfere with the effective transmission of energy from the primary coil to the secondary coil.

Eddy currents cause energy loss from the transformer when heating the core, which means that electrical energy is wasted as excess heat.

Laminating refers to "consisting of insulating layers of iron "glued" together", rather than in a single solid "block." Compared with non-laminated cores having the same number of domains, laminated cores have higher electrical resistance. Therefore, it does not generate such a large current.