Explanation: In a magnetic circuit, the opposition to the establishment of magnetic lines of force (magnetic flux) is known as **reluctance**. It is analogous to electrical resistance in an electrical circuit, where resistance opposes the flow of current. Materials with high reluctance will make it more difficult to create a strong magnetic field. * **Eddy currents** are circulating currents induced within a conductor by a changing magnetic field, causing energy loss and heating, not the fundamental opposition to forming the field itself. * **Hysteresis** describes the lagging of a magnetic material's magnetization behind the applied magnetic field, representing energy loss from reorienting magnetic domains, rather than the initial opposition to flux creation. * **Permeability** is the *measure* of a material's ability to support the formation of a magnetic field within itself. It is the inverse of reluctance – high permeability means low reluctance.