What causes sound waves to vibrate the coil in a microphone?

Sound waves are vibrations that travel through the air (or another medium) as fluctuations in air pressure. When sound waves reach a microphone, they create variations in the air pressure that strike a diaphragm inside the microphone. This diaphragm is attached to a coil in a magnetic field, causing it to move in response to the changes in air pressure.

As the diaphragm vibrates due to the sound waves, it causes the coil to vibrate as well. This movement of the coil within the magnetic field generates an electrical current that corresponds to the sound wave, allowing the microphone to convert sound into an electrical signal. Thus, the correct answer highlights the role of air pressure changes in creating these vibrations that drive the microphone's function.