There is usually a bulky cylinder attached to the end of laptop or mobile device charging cord, ever wondered why? Commonly, keyboard cables also have these cylinders. These cylinders include ferrite beads used to eliminate energy loss in the cord. Sometimes, they are called EMI filters or chokes, but their purpose is to efficiently charge and transfer power.
Large energy loss can occur through electromagnetic interference (EMI), as the current passes through cable. Ferrite beads are usually found near the ends of cables because they are always placed near the source. High-frequency electromagnetic noise is absorbed by a small amount of ferrite ceramic present in each cylinder.
If the ferrite beads which are encased in plastic were cut open, you would find 2 halves of a ferrite ceramic cylinder. They can also stop interference from other signals like cell phones or similar power sources nearby along with stopping energy transmission EMI.