5.1 Waves and Light - Wave properties

A wave is a vibration (an oscillation) that transfers energy from one place to another without transferring matter.

There are two main types of waves you need to know:

Transverse Waves

In a transverse wave, the oscillations are perpendicular (at 90°) to the direction of energy transfer.

• Examples: All electromagnetic waves (like light), ripples on water, waves on a string.

Longitudinal Waves

In a longitudinal wave, the oscillations are parallel to the direction of energy transfer. They show areas of compression (particles close together) and rarefaction (particles spread apart).

• Examples: Sound waves, ultrasound waves.

We can describe waves using these key properties:

• Amplitude: The maximum displacement of a point on the wave from its rest position. (This is related to the wave's energy).
• Wavelength (λ): The distance between one point on a wave and the same point on the next wave (e.g., from one crest to the next). Measured in metres (m).
• Frequency (f): The number of complete waves that pass a point every second. Measured in hertz (Hz).
• Time Period (T): The time it takes for one complete wave to pass a point. Measured in seconds (s).

The Wave Speed (v) is how fast the energy is transferred. It is calculated using the wave equation:

Wave Speed = Frequency × Wavelength

v = f × λ

Where:

• v is wave speed in metres per second (m/s)
• f is frequency in hertz (Hz)
• λ (lambda) is wavelength in metres (m)

All waves can be:

• Reflected: The wave bounces off a surface (like light in a mirror or an echo).
• Refracted: The wave changes speed and bends (changes direction) as it passes from one medium to another (like a straw in a glass of water).
• Transmitted: The wave passes through the material.
• Absorbed: The wave transfers its energy to the material.