A round resistance coil is a laboratory apparatus used to create a known and adjustable electrical resistance. It consists of a spool or bobbin made of an insulating material, around which is wound a long wire made of a high-resistance material, such as nichrome. The wire is coiled evenly around the spool to create a uniform resistance along its length.
The resistance can be adjusted by changing the length of the wire used or by changing the diameter of the coil. Round resistance coils are commonly used in electrical experiments to investigate the relationship between current, voltage, and resistance, and to measure the resistance of other circuit components.