Resonance Graphs (Edexcel International A Level Physics)

A graph of driving frequency f against amplitude A of oscillations is called a resonance curve. It has the following key features:

• When f < f₀, the amplitude of oscillations increases

• At the peak where f = f₀, the amplitude is at its maximum. This is resonance

• When f > f₀, the amplitude of oscillations starts to decrease

Damping reduces the amplitude of resonance vibrations

The height and shape of the resonance curve will therefore change slightly depending on the degree of damping

• Note: the natural frequency f₀ of the oscillator will remain the same

As the degree of damping is increased, the resonance graph is altered in the following ways:

• The amplitude of resonance vibrations decrease, meaning the peak of the curve lowers

• The resonance peak broadens

• The resonance peak moves slightly to the left of the natural frequency when heavily damped

Therefore, damping reduced the sharpness of resonance and reduces the amplitude at resonant frequency