Final answer:
Active detectors generate an electrical signal when interacting with photons, while passive detectors rely on changes caused by photons to form an image.
Step-by-step explanation:
The difference between "active" detectors and "passive" detectors lies in their characteristics. Active detectors are capable of generating an electrical signal when they interact with photons, while passive detectors rely on changes caused by photons and record the points to form an image. For example, photomultiplier tubes in microscopes and CCD cameras are passive detectors that rely on particle-like properties of photons, whereas solid-state radiation detectors convert ionization produced in a semiconductor directly into an electrical signal.