What is essential to the operation of a charge-coupled device (CCD)?

The operation of a charge-coupled device (CCD) is fundamentally based on its ability to transfer charge in response to light exposure. When light photons strike the photosensitive area of the CCD, they generate electron-hole pairs. The device then collects and transfers these charges through a series of capacitive elements. This charge movement is what ultimately creates the electronic representation of the image, allowing the CCD to convert light into an electrical signal that can be further processed and displayed.

In this context, the emphasis on light exposure underscores the nature of how CCDs capture images, as the resulting charge from incident light is the core mechanism in their functionality. This process is central to understanding how CCDs work in various imaging applications, such as cameras and scientific instruments.

The other options address mechanisms or characteristics that do not apply to the operation of CCDs. For instance, reliance on magnetism, chemical reactions for image generation, or operation without any external power source are not relevant to the fundamental principles of how CCDs function.