What device is used to convert sound waves into electric current?

The device that converts sound waves into electric current is indeed often a microphone, which typically operates based on the principles of a transducer. A common type of microphone, known as a dynamic microphone, uses electromagnetic induction to convert the mechanical energy of sound waves into an electrical signal.

While the option chosen was a transformer, which is primarily used to change the voltage level in an electrical circuit, it does not have the function of converting sound waves into electrical current. Instead, the proper connection to this question lies with devices like microphones that fit the description given.

Generators, on the other hand, convert mechanical energy into electrical energy but do not directly involve sound wave input. Capacitors store electrical energy, and transistors amplify or switch electronic signals but are not used for the direct conversion of sound waves.

Thus, understanding the role of sound transducers, particularly microphones, clarifies the concept of how sound can be transformed into electrical signals, pointing towards the fundamentals of audio technology.