Electromagnetic force in loudspeakers

Steps:

• Loudspeakers use alternating current (AC) in a coil within a permanent magnetic field to vibrate a cone and produce sound.
• Evaluate sentence 1: Incorrect, as direct current (DC) would produce steady force, not vibrations; AC is required.
• Evaluate sentence 2: Correct, AC in the coil generates a changing magnetic field that interacts with the permanent field.
• Evaluate sentence 3: Correct, the motor effect (F = BIL sinθ) produces force on the current-carrying coil in the magnetic field.
• Evaluate sentence 4: Incorrect, the cone vibrates linearly due to alternating forces, not spins.

Why C is correct:

• C selects 2 and 3, matching the motor effect where changing current produces force on the coil in a magnetic field (Fleming's left-hand rule).

Why the others are wrong:

• A includes incorrect DC (sentence 1).
• B includes incorrect DC and spinning (sentences 1 and 4).
• D includes incorrect spinning (sentence 4).

Final answer: C