Which term describes the substance through which a wave travels?

• A. Medium
• B. Density
• C. Analog
• D. Digital

Answer: (A)

A wave travels through a medium—the substance that carries the wave’s energy and allows it to propagate. In the medium, particles are set into motion and pass the energy along, which is how the wave moves from one place to another. Sound is a good example: it travels through air, water, or solids because those materials can transmit the vibrating motion. Some waves, like light, can travel through empty space, which shows that a medium isn’t always required, but when a substance is involved, the correct term for that substance is medium. Density is just a property of the material that can influence how fast a wave moves, not the term for the substance itself. Analog and digital describe ways of representing information, not materials through which waves travel.