Which demonstration can illustrate the use of light or sound to solve a communication problem?

The use of paper cup and string telephones is an effective demonstration to illustrate the concept of using sound to solve a communication problem. This simple device conveys sound through vibrations traveling along the string, effectively transforming acoustic energy into mechanical energy and allowing for communication between two points.

When one person speaks into their cup, sound waves travel through the air, causing the bottom of the cup to vibrate. These vibrations are then transferred through the tightly-stretched string to the other cup, where they are converted back into sound waves, allowing the second person to hear the original message. This experiment not only showcases the principles of sound transmission but also emphasizes the idea that communication can occur through alternative methods, demonstrating practical physics in a hands-on way.

In contrast, while the other options involve physical phenomena, they do not specifically illustrate the use of light or sound for communication. The magnet and iron filings demonstrate magnetic fields, solar panels charging a battery relate to energy conversion, and a windmill powered by wind is more about converting kinetic energy than facilitating communication.