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UNIT 9: SENSORS AND ACTUATORS INTRODUCTION Sensors measure physical quantities like temperature, light, or motion. Actuators convert electrical signals into physical actions like movement or sound. Together, they allow electronic systems to interact with the world. STORY 1: Types of Sensors There are many sensors. A temperature sensor (thermistor) changes resistance with heat. A light sensor (photoresistor) changes resistance with light. A proximity sensor detects objects without touching.