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Photoresistors

1a) Two lead photoresistors using a   (2 words)  element show a dramatic (1 word) in resistance when illuminated;  and are commonly used as a light sensing element for security lights, etc. so that they will (2 words) at night.

1b) In the dark, the resistance is very   (1 word), in the (value & unit) range. When illuminated, the resistance may (1 word) to a few hundred ohms. They are typically more sensitive to (1 word) light, and they have a very (1 word) sensitivity compared to other types of sensors.

Photo Detectors

2a) You walk into a store and a bell will go off as you cross the threshold. If you look, you will often notice that a photo beam detector is being used. Near the door on one side of the store is a light (either a (5 words) or a (3 words), and on the other side is a photodetector that can  (1 word) the light.

2b) Inside the photoelectric smoke detector there is a (1 word) and a (1 word), which are positioned at (2 words ) angles to one another.

2c) In the normal case, the light from the light source shoots straight across and misses the sensor. When smoke enters the chamber, however, the smoke particles (1 word) the light and some amount of light hits the (1 word) which then sets off the (1 word) in the smoke detector.