BrightPath Back to Course
Year 11 Science

Introduction to Waves

Understand the nature of waves, the difference between transverse and longitudinal waves, and the key properties of wavelength, frequency, amplitude and wave speed.

Types of Waves

A wave is a disturbance that transfers energy from one place to another without transferring matter. Waves can be classified by the direction of oscillation relative to the direction of energy transfer.

Transverse Waves

Direction of energy →

Oscillation is perpendicular (at right angles) to the direction of energy transfer.

Examples: Light, water surface waves, waves on a string, electromagnetic waves

Longitudinal Waves

Compressions (dense) and rarefactions (spread out)

Oscillation is parallel to the direction of energy transfer.

Examples: Sound waves, pressure waves, seismic P-waves

Important: Waves transfer energy, not matter. The particles of the medium oscillate about their equilibrium position but do not travel with the wave. Only the disturbance propagates.

Wave Properties

All waves can be described by four key properties: wavelength, frequency, amplitude and wave speed. These properties are related by the wave equation.

Wavelength (λ)

The distance between two consecutive identical points on a wave (e.g. crest to crest or trough to trough). Measured in metres (m).

Frequency (f)

The number of complete waves passing a point per second. Measured in hertz (Hz), where 1 Hz = 1 wave per second.

Amplitude (A)

The maximum displacement of a point on the wave from its equilibrium (rest) position. Related to energy -- larger amplitude means more energy.

Period (T)

The time taken for one complete wave cycle to pass a point. Measured in seconds (s). T = 1/f.

The Wave Equation

v = f λ

wave speed (m s-1) = frequency (Hz) × wavelength (m)

v

Wave speed (m s-1)

f

Frequency (Hz)

λ

Wavelength (m)

The Electromagnetic Spectrum

Electromagnetic waves are transverse waves that do not require a medium -- they can travel through a vacuum. All electromagnetic waves travel at the speed of light (c = 3.0 × 108 m s-1) in a vacuum.

Electromagnetic Spectrum (increasing frequency →)

Radio

Longest λ

Micro-wave

Infrared

Visible

Ultra-violet

X-rays

Gamma

Shortest λ

Key relationship: Since all EM waves travel at the same speed in a vacuum, higher frequency means shorter wavelength (and vice versa). v = fλ, so if v is constant and f increases, λ must decrease.

Key Vocabulary

Wavelength (λ)

The distance between successive identical points on a wave, such as crest to crest. Measured in metres.

Frequency (f)

The number of complete oscillations per second. Measured in hertz (Hz). Related to period by f = 1/T.

Compression

A region of high pressure in a longitudinal wave where particles are pushed close together.

Rarefaction

A region of low pressure in a longitudinal wave where particles are spread apart.

Worked Examples

1

A sound wave has a frequency of 440 Hz and a wavelength of 0.77 m. Calculate the speed of sound.

Known: f = 440 Hz, λ = 0.77 m

Using: v = fλ = 440 × 0.77

v = 339 m s-1 (approximately the speed of sound in air)

2

An FM radio station broadcasts at 104.1 MHz. What is the wavelength? (c = 3.0 × 108 m s-1)

Known: f = 104.1 MHz = 104.1 × 106 Hz, v = 3.0 × 108 m s-1

Using: λ = v / f = (3.0 × 108) / (104.1 × 106)

λ = 2.88 m

3

A wave has a period of 0.02 s. What is its frequency?

Known: T = 0.02 s

Using: f = 1 / T = 1 / 0.02

f = 50 Hz

Knowledge Check

Select the correct answer for each question. Click "Check Answer" to see if you are right.

Question 1

In a transverse wave, the particles oscillate:

Question 2

Sound is an example of a:

Question 3

A wave has a frequency of 500 Hz and a wavelength of 0.68 m. What is its speed?

Question 4

If the frequency of a wave doubles but the speed stays the same, the wavelength:

Question 5

Which property of a wave is most directly related to the energy it carries?

Key Concepts Summary

Year 11: DNA Structure Year 11: Moles & Stoichiometry