Topic 13: Oscillations — Edexcel A-Level Physics
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Topic 13: Oscillations explained
Resonance occurs when a system is driven by a periodic force whose frequency matches the system's natural frequency.
Read the full explanation
At this matching frequency the amplitude of oscillation reaches a maximum because energy is transferred most efficiently from the driver to the oscillator each cycle. The natural frequency depends on the system, for example the length of a pendulum or the mass and stiffness of a spring–mass system. A graph of amplitude against driving frequency peaks sharply at the natural frequency; increased damping lowers and broadens this peak. Resonance explains phenomena such as a swing pushed in time with its motion, or a glass shattering at a particular note. It is not simply any large vibration: the defining feature is the driving frequency equalling the natural frequency, producing maximum amplitude.
Your focus
- Define resonance in terms of driving frequency matching natural frequency.
- Explain why amplitude is maximum at resonance through efficient energy transfer.
- Describe how damping changes the amplitude–frequency resonance curve.
Topic 13: Oscillations exam tips
Marking Points
- Resonance is the large-amplitude response of a system driven at a frequency equal to its natural frequency.
- At resonance the driving frequency matches the natural frequency, so energy is transferred efficiently and amplitude is maximum.
- The natural frequency is a property of the system, such as the length of a pendulum or the mass and stiffness of a spring–mass oscillator.
- An amplitude–frequency graph peaks at the natural frequency, and increased damping reduces and broadens the peak.
- Resonance requires a periodic driving force; without a driver matching the natural frequency the maximum response does not occur.
Examiner Tips
- 💡State both conditions: a periodic driving force and a driving frequency equal to the natural frequency.
- 💡Link maximum amplitude to efficient energy transfer from the driver to the oscillator.
- 💡Use an amplitude–frequency graph to show the peak at the natural frequency and the effect of damping.
Common Mistakes
- Defining resonance as any large oscillation: the key condition is the driving frequency equalling the natural frequency.
- Confusing natural frequency with driving frequency: the natural frequency belongs to the system, while the driving frequency is imposed externally.
- Claiming damping increases the resonant amplitude: greater damping lowers and broadens the peak rather than raising it.