Resonance has what effect on the amplitude of a vibrating system when driven at its natural frequency?

• A. Decreased amplitude
• B. No effect
• C. Increased amplitude
• D. Random amplitude

Answer: (C)

When a system is driven at its natural frequency, it resonates. That means the driving force adds energy to the motion in step with the vibration, so the energy input accumulates and the amplitude grows. In a real system, damping limits how large the amplitude can get, but the peak response at the natural frequency is still much larger than at other frequencies. So, resonance increases the amplitude of the vibrating system when driven at its natural frequency.