Which of the following describes a Passive device?

A passive device is characterized by its ability to operate without the need for an external power source or voltage. This means that it does not require any supplied electrical energy to function, instead relying on the electrical signals or currents that pass through it.

For instance, passive devices include components like resistors, capacitors, and inductors. These components can influence signals by filtering, attenuating, or altering their properties, but they do not generate or amplify signals.

In contrast, other options indicate active functions. For example, a device that requires voltage to operate suggests that it is active, as it depends on an external power source for its functionality. Similarly, devices that convert electrical energy to light, such as LEDs, are active components because they perform work on the electrical energy. Lastly, heating up when current flows indicates a device that dissipates energy, typical of active components, as passive devices do not actively generate heat when current passes through them.

Thus, the defining feature of a passive device is its ability to function solely based on the signals passing through it, which accurately aligns with the description of not requiring a voltage.