Magnetic effect of current in devices

Steps:

• Identify the magnetic effect: Electric current generates a magnetic field, as per Oersted's discovery.
• Evaluate each option: Check if the device relies on current-induced magnetism for operation.
• Eliminate non-magnetic devices: Rulers out those using heat, light, or Earth's field.
• Confirm the match: Select the device using current in a coil to create magnetic force.

Why C is correct:

• Loudspeakers use an electromagnet where current in a coil produces a magnetic field that interacts with a permanent magnet, causing the cone to vibrate and produce sound (Faraday's law of electromagnetic induction).

Why the others are wrong:

• A. Compass detects Earth's magnetic field, not current-induced magnetism.
• B. Fuse melts from current's heat via Joule heating, not magnetic effects.
• D. Magnifying glass bends light through refraction, unrelated to electricity or magnetism.

Final answer: C