By altering the length of the runner, you can optimize the resonance effect.

• A. Length
• B. Diameter
• C. Material
• D. Cross-section

Answer: (A)

Resonance depends on the path length that the wave can fit inside the system. The length of the runner determines which wavelengths can form a standing wave and thus meet the resonance condition. By changing that length, you adjust the allowed standing-wave modes and move the system onto or away from a resonant state, maximizing the resonance effect when the length lines up with a multiple of half-wavelengths. Diameter, material, or cross-section mainly affect how strongly or quickly the wave is damped and how easily it propagates, which changes the sharpness or strength of resonance but not the basic frequency that can resonate for a given mode. So adjusting the length is the direct way to optimize resonance.