Sound waves are vibrations that cause the diaphragm to vibrate back and forth. The coil is attached to the diaphragm, so it also moves back and forth within the magnetic field of the magnet. As the coil moves, it cuts magnetic field lines, which induces a potential difference across the ends of the coil. This potential difference creates an alternating current in the electric circuit that has the same frequency as the sound wave.
A moving-coil microphone converts sound energy into electrical energy using the principle of electromagnetic induction.
1. **Vibration:** The incoming sound waves consist of compressions and rarefactions, which are pressure variations. These variations exert a changing force on the diaphragm, causing it to vibrate back and forth.
2. **Coil Movement:** Since the coil of wire is attached to the diaphragm, it vibrates with the same pattern as the sound wave.
3. **Electromagnetic Induction:** The microphone contains a permanent magnet that creates a magnetic field. As the coil moves back and forth within this field, the wire cuts through the magnetic field lines.
4. **Induced Current:** This cutting of field lines induces a potential difference (voltage) across the ends of the coil. Because the coil is part of a complete circuit, this potential difference drives an alternating current that mirrors the vibrations of the sound wave. This electrical signal can then be amplified and recorded.
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