Explain how the photoelectric effect is used to open automatic doors when someone approaches.?
You have a photoelectric sensor near the door which detects say infrared light. You then include a tiny infrared transmitter near the detector which sends out a low amount of infrared light. When someone comes within say 1m of the car, they step infront of the beam and some of the energy reflects back and is detected by the sensor. At which point, electronics trigger a motor which unlocks/opens the car door. Software in the electronics might included timing logic and/or determine if the reflected signal is getting stronger (i.e. someone is moving near) in order to not open the door if someone say moves past.
