Question 56 CEL01 - Chief Engineer - Limited

The Correct Answer is B **Explanation for Option B (Correct):** Resonance is the phenomenon that occurs when a vibrating system (like a piece of machinery) is subjected to a driving force (external vibration) whose frequency is equal or very close to the system's own natural frequency (or one of its natural frequencies). When this condition is met, the system absorbs energy very efficiently, causing a rapid buildup of vibration amplitude. This large, sustained amplitude can lead to catastrophic failure, justifying why resonance is a major concern in machinery operation and design. **Explanation for Other Options (Incorrect):** * **A) The natural frequency of the machinery is the same as the free vibration frequency.** * This statement is tautological (self-referential). Free vibration is defined as the vibration that occurs at the natural frequency when no external force is acting. This condition describes the *definition* of the natural frequency, but it does not describe the *cause* of destructive resonance, which requires an external driving force. * **C) The machinery is operated at the natural frequency with no external forces in play.** * If there are no external forces (no driving force), the machinery will undergo **free vibration**. Since all real-world systems have damping, this vibration will quickly die out. Resonance requires a continuous input of energy via an external force vibrating at the natural frequency to sustain and amplify the destructive amplitude. * **D) A forced frequency is placed on a piece of operating machinery.** * This condition describes **forced vibration**, but it does not necessarily cause resonance. Forced vibration simply means there is an external driving force. If the frequency of this forced vibration is significantly different from the natural frequency of the machinery, the resulting vibrations will be minor and stable, not leading to destructive resonance. Resonance only occurs in the specific (and dangerous) case where the forced frequency matches the natural frequency (Option B).