What device is placed in line with the load to limit current in an electrical circuit?

The device that is placed in line with the load to limit current in an electrical circuit is a ballast. A ballast is typically used in lighting applications, particularly with fluorescent and HID lamps, to control the starting and operating current to the lamps. By regulating the current, a ballast ensures that the lamp operates within its specified parameters, preventing excessive current that could lead to overheating or premature failure.

Ballasts work by providing the necessary voltage to start the lamp and then limiting the current to maintain proper operation once the lamp is lit. This current limiting action is crucial for the stability and efficiency of the circuit.

The other options are not used for this purpose. A discharger, for example, is related to circuitry that discharges stored energy, and diodes are semiconductor devices that allow current to flow in one direction only, primarily used for rectification. Cathodes refer to electrodes where reduction reactions occur in electrochemical cells or vacuum tubes, but they do not serve the function of limiting current in electrical circuits.