The number of electron/hole pairs in a CCD is related to the amount of:

• A. Light absorbed
• B. Light emitted
• C. X-ray energy
• D. Time

Answer: (A)

In a CCD, electrons and holes are created when photons are absorbed by the silicon. Each absorbed photon above the bandgap can generate an electron-hole pair, so the total number of pairs is proportional to how much light is actually absorbed (not just incident light). The device’s signal also depends on quantum efficiency—the fraction of absorbed photons that produce a carrier. Light that is emitted wouldn’t create carriers in the detector, X-ray energy isn’t the typical optical signal for a standard CCD, and while longer exposure time means more photons can be collected, the fundamental link is the amount of light actually absorbed.