Final answer:
The Echo pin on the HC-SR04 ultrasonic sensor is utilized to receive ultrasonic wave reflections, which are then used to calculate the distance to objects. b) Receives ultrasonic wave reflections
Step-by-step explanation:
The function of the HC-SR04 pin labeled Echo is to receive ultrasonic wave reflections. When using an ultrasonic sensor like the HC-SR04, a signal is sent out by the Trigger pin as ultrasonic sound waves. These sound waves bounce off objects and return to the sensor. The Echo pin is responsible for capturing the reflected sound waves, which can then be used to calculate the distance to the object based on the time it took for the echo to return. This technology is similar to how ultrasound in medical settings operates, with echoes being recorded and measured to construct images of internal structures, or how radar determines the distance to objects by measuring echo times. The HC-SR04 ultrasonic sensor has two main pins related to its operation: Trig (Trigger) and Echo. When triggered, the sensor sends out ultrasonic waves (sound waves at a frequency too high for humans to hear). The Echo pin is responsible for receiving the reflections of these ultrasonic waves. By measuring the time it takes for the ultrasonic waves to travel to an object and back, the sensor can calculate the distance to the object. Therefore, option (b) "Receives ultrasonic wave reflections" accurately describes the function of the Echo pin on the HC-SR04 sensor.