A capacitive sensor uses the principle of __________ to sense the presence of an object.

• A. Induction
• B. Capacitance
• C. Resonance
• D. Thermionic emission

Answer: (B)

Capacitance change in the sensing region is what capacitive sensors rely on to detect an object's presence. The capacitance between two conductors depends on the dielectric material between them and their geometry, so when an object with a different dielectric constant enters or moves closer to the sensing area, the effective capacitance changes and the sensor recognizes that something is there. This principle enables detection of both conductive and non-conductive materials without contact. The other options describe different sensing methods—induction uses magnetic coupling to detect metal objects, resonance detects shifts in a resonant circuit, and thermionic emission concerns electron emission from heated materials. So, the sensing mechanism here is based on capacitance.