CIE IGCSE PHYSICS

TOPIC 3.1 – GENERAL PROPERTIES OF WAVES

INTRODUCTION TO WAVES

Waves are oscillations or vibrations about a fixed point.

Waves transfer energy and information.

In general, waves transfer energy without transferring matter.

For example, objects floating on water move up and down as waves pass but do not

travel with the wave itself.

FEATURES OF WAVES

Crest (Peak):

The highest point on a wave above the equilibrium (rest) position.

Trough:

The lowest point on a wave below the equilibrium (rest) position.

Amplitude:

The maximum distance from the equilibrium position to the crest or trough of a wave.

Unit: metres (m).

Wavelength (λ):

The distance between two identical points on a wave, such as crest to crest or trough to trough.

Unit: metres (m).

Frequency (f):

The number of complete waves passing a point per second.

Unit: hertz (Hz).

Wavefront:

A line drawn to represent the crests of a wave in two dimensions.

The distance between adjacent wavefronts is equal to one wavelength.

THE WAVE EQUATION

Wave speed is the distance travelled by a wave per second.

v = f × λ

Where:

v = wave speed (m/s)

f = frequency (Hz)

λ = wavelength (m)

Time Period:

T = 1 / f

Where:

T = time period in seconds (s)

WORKED EXAMPLES

Example 1:

A radio wave has a wavelength of 250 m and travels at a speed of 3.0 × 10⁸ m/s.

f = v / λ

f = (3.0 × 10⁸) / 250

f = 1.2 × 10⁶ Hz (1.2 MHz)

Example 2:

A wave has a speed of 0.15 m/s and a time period of 2 s.

Frequency:

f = 1 / T

f = 1 / 2

f = 0.5 Hz

Wavelength:

λ = v / f

λ = 0.15 / 0.5

λ = 0.30 m

TRANSVERSE AND LONGITUDINAL WAVES

Transverse Waves:

In transverse waves, the particles vibrate perpendicular to the direction of wave travel.

Key points:

• Energy transfer is perpendicular to wave motion

• Particles vibrate but do not move with the wave

• Can travel in solids and on the surface of liquids

• Electromagnetic waves can travel through solids, liquids, gases, and a vacuum

Examples:

• Light waves

• Radio waves

• Water waves

• S-waves

Longitudinal Waves:

In longitudinal waves, the particles vibrate parallel to the direction of wave travel.

Key points:

• Energy transfer is in the same direction as wave motion

• Particles vibrate but do not move with the wave

• Can travel through solids, liquids, and gases

• Cannot travel through a vacuum

Key features:

• Compressions – particles are close together

• Rarefactions – particles are far apart

Examples:

• Sound waves

• P-waves

• Pressure waves

COMPARISON OF TRANSVERSE AND LONGITUDINAL WAVES

Property: Structure

Transverse: Crests and troughs

Longitudinal: Compressions and rarefactions

Property: Direction of vibration

Transverse: Perpendicular to wave travel

Longitudinal: Parallel to wave travel

Property: Travel through vacuum

Transverse: Only electromagnetic waves can travel

Longitudinal: Cannot travel

Property: Density

Transverse: Constant

Longitudinal: Changes

Property: Pressure

Transverse: Constant

Longitudinal: Changes

WAVE BEHAVIOUR

All waves can undergo reflection, refraction, and diffraction.

Reflection:

Reflection is the bouncing back of a wave from a surface such as a wall or mirror.

Law of Reflection:

Angle of incidence = Angle of reflection

Refraction:

Refraction occurs when a wave changes direction due to a change in speed as it moves from one medium to another.

During refraction:

• Speed changes

• Wavelength changes

• Direction changes

• Frequency remains constant

Diffraction:

Diffraction is the spreading out of waves when they pass through a narrow gap or around an obstacle.

Diffraction is most noticeable when:

• The gap is similar in size to the wavelength

• The gap is smaller than the wavelength

As the gap becomes much larger than the wavelength, diffraction becomes less noticeable.

RIPPLE TANK

Ripple tanks are used to demonstrate the properties of water waves, including:

• Reflection

• Refraction

• Diffraction through a gap

• Diffraction around an edge

By Noella Gracious Mulungi

curated by Yassein Abdoun