Final answer:
The acoustical phenomenon used to create sound in the Theremin is resonance.
Step-by-step explanation:
The acoustical phenomenon used to create sound in the Theremin is resonance. Resonance is a phenomenon that occurs when an object vibrates at its natural frequency in response to the frequency of an external force or source. In the case of the Theremin, the instrument consists of two antennas, one for controlling pitch and the other for controlling volume. The musician interacts with the instrument by moving their hands near these antennas, which alters the capacitance and thus the frequency of the oscillators, creating sound through resonance.