CIE A Level Physics (9702) exams from 2022

Revision Notes

17.1.1 Describing Oscillations

Describing Oscillations

  • An oscillation is defined as:

Repeated back and forth movements on either side of any equilibrium position

  • When the object stops oscillating, it returns to its equilibrium position
    • An oscillation is a more specific term for a vibration
    • An oscillator is a device that works on the principles of oscillations
  • Oscillating systems can be represented by displacement-time graphs similar to transverse waves
  • The shape of the graph is a sine curve
    • The motion is described as sinusoidal

Properties of Oscillations

  • Displacement (x) of an oscillating system is defined as:

The distance of an oscillator from its equilibrium position

  • Amplitude (x0) is defined as:

The maximum displacement of an oscillator from its equilibrium position

  • Angular frequency (⍵) is defined as:

The rate of change of angular displacement with respect to time

  • This is a scalar quantity measured in rad s-1 and is defined by the equation:

Describing Oscillations equation 1

  • Frequency (f) is defined as:

The number of complete oscillations per unit time

  • It is measured in Hertz (Hz) and is defined by the equation:

Describing Oscillations equation 2

  • Time period (T) is defined as:

The time taken for one complete oscillation, in seconds

  • One complete oscillation is defined as:

 The time taken for the oscillator to pass the equilibrium from one side and back again fully from the other side

  • The time period is defined by the equation:

Describing Oscillations equation 3

  • Phase difference is how much one oscillator is in front or behind another
    • When the relative position of two oscillators are equal, they are in phase
    • When one oscillator is exactly half a cycle behind another, they are said to be in anti-phase
    • Phase difference is normally measured in radians or fractions of a cycle
    • When two oscillators are in antiphase they have a phase difference of π radians

Worked example: Calculating angular frequency

Step 1:           

Write down the equation for angular frequency

Describing Oscillations Worked Example equation 1

Step 2:           

Calculate the time period T from the graph

The time period is defined as the time taken for one complete oscillation

This can be read from the graph:

T = 2.6 − 0.5 = 2.1 s

Step 3:

Substitute into angular frequency equation

Describing Oscillations Worked Example equation 2

Exam Tip

The properties used to describe oscillations are very similar to transverse waves. The key difference is that oscillators do not have a ‘wavelength’ and their direction of travel is only kept within the oscillations themselves rather than travelling a distance in space.

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