Photoelectric sensors operate on the principle of which?

• A. Piezoelectric effect
• B. Photoconduction
• C. Electromagnetic induction
• D. Thermoelectric effect

Answer: (B)

Photoelectric sensors rely on light altering the electrical conduction in a material. When the photosensitive semiconductor is illuminated, photons excite electrons and create electron‑hole pairs, which increases the material’s conductivity. This change in current or resistance is what the sensor detects to indicate presence or absence of an object (as light is interrupted, reflected, or transmitted).

The other effects don’t describe how these sensors operate. The piezoelectric effect is about voltage generated from mechanical stress, not light. Electromagnetic induction involves voltage from changing magnetic fields, not light-induced conduction. The thermoelectric effect uses temperature differences to generate voltage, not light-driven changes in conductivity.