Electromagnetic force drives vibration in loudspeakers

Steps:

• Varying current in the coil produces a changing magnetic field.
• This field interacts with the permanent magnet, exerting a force on the coil via the motor effect.
• The coil, attached to the cone, transfers its vibration to the cone.
• The cone's vibration displaces air molecules, generating sound waves.

Why D is correct:

• In loudspeakers, the coil vibrates due to the Lorentz force (F = BIL sinθ) from the current in the magnetic field, and the attached cone vibrates to amplify air displacement for audible sound.

Why the others are wrong:

• A: Coil vibrates but cannot produce sound alone without the cone displacing air.
• B: Cone vibrates but is driven by the coil's motion, not independently.
• C: Magnet provides a static field and does not vibrate.

Final answer: D