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CAIE A-Level Physics 17.3 Damping and Resonance

Practise explaining damping, classifying light, critical and heavy damping, interpreting decay and resonance under forced oscillation.

Syllabus
2028–2030
Course
Physics 9702
Level
A2

Exam points

  • explain damping and distinguish light, critical and heavy damping from graphs or behaviour
  • interpret damping graphs and energy/amplitude decay
  • explain resonance as maximum forced amplitude at the natural frequency and analyse the effects of driving frequency and damping

Covered syllabus points

17.3.1—A resistive force acting on an oscillating system causes damping17.3.2—The terms light, critical and heavy damping and sketch displacement–time17.3.3—Resonance involves a maximum amplitude of oscillations and that this occurs

17.3 Damped and forced oscillations, resonance question 1

[Maximum number: 1]

A small wooden block (cuboid) of mass m floats in water, as shown in Fig. 3.1.

Fig. 3.1

Fig. 3.1

The top face of the block is horizontal and has area A. The density of the water is ρ\rho.

The block is now placed in a liquid with a greater density. The block is displaced and released so that it oscillates vertically. The variation with displacement x of the acceleration a of the block is measured for the first half oscillation, as shown in Fig. 3.3.

Fig. 3.3

Fig. 3.3

Explain why the maximum negative displacement of the block is not equal to its maximum positive displacement.

17.3 Damped and forced oscillations, resonance question 2

[Maximum number: 2]

An object is suspended from a vertical spring as shown in Fig. 3.1.

Fig. 3.1

Fig. 3.1

The object is displaced vertically and then released so that it oscillates, undergoing simple harmonic motion.

Fig. 3.2 shows the variation with displacement x of the energy E of the oscillations.

Fig. 3.2 shows the variation with displacement x of the energy E of the oscillations.

Fig. 3.2

The kinetic energy, the potential energy and the total energy of the oscillations are each represented by one of the lines P, Q and R .

Question (a)

(a)

State the cause of damping.

[ 1 ]

Question (b)

(b)

State, with a reason, the type of damping that the card introduces into the system.

[ 1 ]

17.3 Damped and forced oscillations, resonance question 3

[Maximum number: 3]

Question (a)

(a)

The oscillator in (b) is switched on. The frequency of oscillation of the oscillator is varied, keeping its amplitude of oscillation constant.

The amplitude of oscillation of the trolley is seen to vary. The amplitude is a maximum at the frequency calculated in (b).

[ 3 ]

Question (i)

(i)

State the name of the effect giving rise to this maximum.

[ 1 ]

Question (ii)

(ii)

At any given frequency, the amplitude of oscillation of the trolley is constant.

Explain how this indicates that there are resistive forces opposing the motion of the trolley.

[ 2 ]
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