Final answer:
The 45 Hz ultrasonic pulse-emitting device used in physics labs for noninvasive diagnostics is known as a (d) ultrasonic transducer.
Step-by-step explanation:
The device used in a physics lab for sending and receiving 45 Hz ultrasonic pulses is called an ultrasonic transducer. Ultrasound refers to sound waves with frequencies higher than the highest frequency detectable by the human ear. These ultrasonic waves are utilized in noninvasive medical diagnoses such as fetal monitoring in the womb.
Moreover, when combined with the principles of Doppler shift, these devices become crucial for medical diagnoses to determine velocity and detect motion by evaluating the changes in frequency of echoed sound waves.
Therefore, the correct answer to the question is option (d) Ultrasonic Transducer.