A wine glass can shatter when exposed to a sound wave at a particular frequency. Explain why the glass shatters at this frequency and not at other frequencies, and describe what happens to the amplitude of vibration of the glass as the frequency of the sound approaches this particular frequency.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
When a singer produces a sustained note at just the right frequency, a wine glass can be made to shatter.
Model answer (5 marks)
The glass shatters when the sound wave frequency matches the natural frequency of the glass.
At this frequency the condition of resonance is satisfied.
Because the driving frequency equals the natural frequency, energy is transferred to the glass most efficiently and the glass absorbs maximum energy.
At frequencies away from the natural frequency the amplitude of vibration is much smaller and less energy is transferred.
As the driving frequency approaches the natural frequency the amplitude of vibration of the glass increases and reaches a maximum at the natural frequency.
At this frequency the condition of resonance is satisfied.
Because the driving frequency equals the natural frequency, energy is transferred to the glass most efficiently and the glass absorbs maximum energy.
At frequencies away from the natural frequency the amplitude of vibration is much smaller and less energy is transferred.
As the driving frequency approaches the natural frequency the amplitude of vibration of the glass increases and reaches a maximum at the natural frequency.
Examiner tips
- Use the term "resonance" and "natural frequency". Show that energy transfer is greatest at resonance. Explain the amplitude increase as frequency approaches the natural frequency.
Common mistakes
- Confusing the natural frequency with the frequency of the sound. Failing to mention resonance. Not describing the amplitude change as the frequency approaches the natural frequency.
Mark scheme (5 marks)
- The particular frequency matches the natural frequency of the wine glass
- This condition is called resonance
- At resonance, the driving frequency matches the natural frequency so energy is transferred to the glass most efficiently / the glass absorbs maximum energy
- At frequencies away from the natural frequency, the amplitude of vibration is much smaller / less energy is transferred
- As the driving frequency approaches the natural frequency, the amplitude of vibration of the glass increases (and reaches a maximum at the natural frequency)
Key terms in this question
Related
- All AQA A-Level Physics (7408) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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