Edexcel International A Level Physics

Revision Notes

5.24 Resonance

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  • The frequency of forced oscillations is referred to as the driving frequency, f, or the frequency of the applied force
  • All oscillating systems have a natural frequency, f0, this is defined as the frequency of an oscillation when the oscillating system is allowed to oscillate freely
    • Oscillating systems can exhibit a property known as resonance


  • When the driving frequency approaches the natural frequency of an oscillator, the system gains more energy from the driving force
    • Eventually, when they are equal, the oscillator vibrates with its maximum amplitude, this is resonance
  • Resonance is defined as:

When the frequency of the applied force to an oscillating system is equal to its natural frequency, the amplitude of the resulting oscillations increases significantly

  • For example, when a child is pushed on a swing:
    • The swing plus the child has a fixed natural frequency
    • A small push after each cycle increases the amplitude of the oscillations to swing the child higher. This frequency at which this push happens is the driving frequency
    • When the driving frequency is exactly equal to the natural frequency of the swing oscillations, resonance occurs
    • If the driving frequency does not quite match the natural frequency, the amplitude will increase but not to the same extent as when resonance is achieved
  • This is because, at resonance, energy is transferred from the driver to the oscillating system most efficiently
    • Therefore, at resonance, the system will be transferring the maximum kinetic energy possible

Resonance Effects

  • Resonance occurs for any forced oscillation where the frequency of the driving force is equal to the natural frequency of the oscillator
  • Examples include:
    • An organ pipe, where air resonates down an air column setting up a stationary wave in the pipe
    • Glass smashing from a high pitched sound wave at the right frequency
    • A radio tuned so that the electric circuit resonates at the same frequency as the specific broadcast

Stationary Wave Organ Resonance, downloadable AS & A Level Physics revision notes

Standing waves forming inside an organ pipe from resonance

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